Method for production of vitamin C

ABSTRACT

The present invention relates to newly identified genes that encode proteins that are involved in the synthesis of L-ascorbic acid (hereinafter also referred to as Vitamin C). The invention also features polynucleotides comprising the full-length polynucleotide sequences of the novel genes and fragments thereof, the novel polypeptides encoded by the polynucleotides and fragments thereof, as well as their functional equivalents. The present invention also relates to the use of the polynucleotides and polypeptides as biotechnological tools in the production of Vitamin C from microorganisms, whereby a modification of the polynucleotides and/or encoded polypeptides has a direct or indirect impact on yield, production, and/or efficiency of production of the fermentation product in the microorganism. Also included are methods/processes of using the polynucleotides and modified polynucleotide sequences to transform host microorganisms. The invention also relates to genetically engineered microorganisms and their use for the direct production of Vitamin C.

This application is a continuation of application Ser. No. 11/991,399filed Jul. 3, 2008 (published as US2008/0274520-A1 on Nov. 6, 2008)(abandoned), which is the U.S. national phase under 35 USC 371 ofInternational Application No. PCT/EP2006/008706 filed 7 Sep. 2006 whichdesignated the U.S. and claims priority to European Patent ApplicationNo. 05021368.5 filed 8 Sep. 2005; the entire contents of each of whichare hereby incorporated by reference.

The present invention relates to newly identified genes that encodeproteins that are involved in the synthesis of L-ascorbic acid(hereinafter also referred to as Vitamin C). The invention also featurespolynucleotides comprising the full-length polynucleotide sequences ofthe novel genes and fragments thereof, the novel polypeptides encoded bythe polynucleotides and fragments thereof, as well as their functionalequivalents. The present invention also relates to the use of saidpolynucleotides and polypeptides as biotechnological tools in theproduction of Vitamin C from microorganisms, whereby a modification ofsaid polynucleotides and/or encoded polypeptides has a direct orindirect impact on yield, production, and/or efficiency of production ofthe fermentation product in said microorganism. Also included aremethods/processes of using the polynucleotides and modifiedpolynucleotide sequences to transform host microorganisms. The inventionalso relates to genetically engineered microorganisms and their use forthe direct production of Vitamin C.

Vitamin C is one of very important and indispensable nutrient factorsfor human beings. Vitamin C is also used in animal feed even though somefarm animals can synthesize it in their own body.

For the past 70 years, Vitamin C has been produced industrially fromD-glucose by the well-known Reichstein method. All steps in this processare chemical except for one (the conversion of D-sorbitol to L-sorbose),which is carried out by microbial conversion. Since its initialimplementation for industrial production of Vitamin C, several chemicaland technical modifications have been used to improve the efficiency ofthe Reichstein method. Recent developments of Vitamin C production aresummarized in Ullmann's Encyclopedia of Industrial Chemistry, 5^(th)Edition, Vol. A27 (1996), pp. 547ff.

Different intermediate steps of Vitamin C production have been performedwith the help of microorganisms or enzymes isolated therefrom. Thus,2-keto-L-gulonic acid (2-KGA), an intermediate compound that can bechemically converted into Vitamin C by means of an alkalinerearrangement reaction, may be produced by a fermentation processstarting from L-sorbose or D-sorbitol, by means of strains belonginge.g. to the Ketogulonicigenium or Gluconobacter genera, or by analternative fermentation process starting from D-glucose, by means ofrecombinant strains belonging to the Gluconobacter or Pantoea genera.

Current chemical production methods for Vitamin C have some undesirablecharacteristics such as high-energy consumption and use of largequantities of organic and inorganic solvents. Therefore, over the pastdecades, other approaches to manufacture Vitamin C using microbialconversions, which would be more economical as well as ecological, havebeen investigated.

Direct Vitamin C production from a number of substrates includingD-sorbitol, L-sorbose and L-sorbosone has been reported in severalmicroorganisms, such as algae, yeast and acetic acid bacteria, usingdifferent cultivation methods. Examples of known bacteria able todirectly produce Vitamin C include, for instance, strains from thegenera of Gluconobacter, Gluconacetobacter, Acetobacter,Ketogulonicigenium, Pantoea, Pseudomonas or Escherichia. Examples ofknown yeast or algae include, e.g., Candida, Saccharomyces,Zygosaccharomyces, Schizosaccharomyces, Kluyveromyces or Chlorella.

Microorganisms able to assimilate D-sorbitol for growth usually possessenzymes able to oxidize this compound into a universal assimilationsubstrate such as D-fructose. Also microorganisms able to grow onL-sorbose possess an enzyme, NAD(P)H-dependent L-sorbose reductase,which is able to reduce this compound to D-sorbitol, which is thenfurther oxidized into D-fructose. D-fructose is an excellent substratefor the growth of many microorganisms, after it has been phosphorylatedby means of a D-fructose kinase.

For instance, in the case of acetic acid bacteria, which are obligateaerobe, gram-negative microorganisms belonging to the genus Acetobacter,Gluconobacter, and Gluconacetobacter, these microorganisms are able totransport D-sorbitol into the cytosol and convert it into D-fructose bymeans of a cytosolic NAD-dependent D-sorbitol dehydrogenase. Someindividual strains, such as Gluconobacter oxydans IFO 3292, and IFO3293, are able as well to transport L-sorbose into the cytosol andreduce it to D-sorbitol by means of a cytosolic NAD(P)H-dependentL-sorbose reductase, which then is further oxidized into D-fructose. Inthese bacteria, the Embden-Meyerhof-Parnas pathway, as well as thetricarboxyclic acid cycle are not fully active, and the main pathwaychanneling sugars into the central metabolism is the pentose phosphatepathway. D-fructose-6-phosphate, obtained from D-fructose by aphosphorylation reaction enters the pentose phosphate pathway, beingfurther metabolized and producing reducing power in the form of NAD(P)Hand tricarboxylic compounds necessary for growth and maintenance.

Acetic acid bacteria are well known for their ability to incompletelyoxidize different substrates such as alcohols, sugars, sugar alcoholsand aldehydes. These processes are generally known as oxidativefermentations or incomplete oxidations, and they have been wellestablished for a long time in the food and chemical industry,especially in vinegar and in L-sorbose production. A useful productknown to be obtained from incomplete oxidations of D-sorbitol orL-sorbose using strains belonging to the Gluconobacter genus is 2-KGA.

Acetic acid bacteria accomplish these incomplete oxidation reactions bymeans of different dehydrogenases located either in the periplasmicspace, on the periplasmic membrane as well as in the cytoplasm.Different co-factors are employed by the different dehydrogenases, themost common being PQQ and FAD for membrane-bound or periplasmic enzymes,and NAD/NADP for cytoplasmic enzymes.

While all products of these oxidation reactions diffuse back to theexternal aqueous environment through the outer membrane, some of themcan be passively or actively transported into the cell and be furtherused in metabolic pathways responsible for growth and energy formation.Inside the cell, oxidized products can many times be reduced back totheir original substrate by means of reductases, and then be channeledback to the central metabolism.

Proteins, in particular enzymes and transporters, that are active in themetabolization of D-sorbitol or L-sorbose are herein referred to asbeing involved in the Sorbitol/Sorbose Metabolization System. Suchproteins are abbreviated herein as SMS proteins and function in thedirect metabolization of D-sorbitol or L-sorbose.

Metabolization of D-sorbitol or L-sorbose includes on one side theassimilation of these compounds into the cytosol and further conversioninto metabolites useful for assimilation pathways such as theEmbden-Meyerhof-Parnas pathway, the pentose phosphate pathway, theEntner-Doudoroff pathway, and the tricarboxyclic acid cycle, all of theminvolved in all vital energy-forming and anabolic reactions necessaryfor growth and maintenance of living cells. On the other side,metabolization of D-sorbitol or L-sorbose also includes the conversionof these compounds into further oxidized products such as L-sorbosone,2-KGA and Vitamin C by so-called incomplete oxidation processes.

An object of the present invention is to improve the yields and orproductivity of Vitamin C production.

Surprisingly, it has now been found that SMS proteins or subunits ofsuch proteins having activity towards or which are involved in theassimilation Or conversion of D-sorbitol, L-sorbose or L-sorbosone playan important role in the biotechnological production of Vitamin C and/or2-KGA.

In one embodiment, SMS proteins of the present invention are selectedfrom oxidoreductases [EC 1], preferably oxidoreductases acting on theCH—OH group of donors [EC 1.1], more preferably oxidoreductases withNAD⁺ or NADP⁺ as acceptor [EC 1.1.1] and oxidoreductases with otheracceptors [EC 1.1.99], most preferably selected from oxidoreductasesbelonging to enzyme classes [EC 1.1.1.1], [EC 1.1.1.15] or [EC 1.2.1.-],or preferably oxidoreductases acting on the aldehyde or oxo group ofdonors [EC 1.2], more preferably oxidoreductases with NAD⁺ or NADP⁺ asacceptor [EC 1.2.1].

Furthermore, the SMS proteins of the present invention may be selectedfrom the group consisting of membrane-bound PQQ-dependent D-sorbitoldehydrogenase, membrane-bound L-sorbose dehydrogenase, membrane-boundL-sorbosone dehydrogenase, membrane-bound FAD-dependent D-sorbitoldehydrogenase, cytosolic NAD-dependent D-sorbitol dehydrogenase,NAD(P)-dependent D-sorbitol dehydrogenase (also called asNADPH-dependent sorbose reductase), NAD-dependent xylitol dehydrogenase,NAD-dependent alcohol dehydrogenase, membrane-bound L-sorbosedehydrogenase, NAD(P)H-dependent L-sorbose reductase, cytosolicNADP-dependent sorbosone dehydrogenase, cytosolic NAD(P)H-dependentL-sorbosone reductase, membrane-bound aldehyde dehydrogenase, cytosolicaldehyde dehydrogenase, glycerol-3-phosphate dehydrogenase,glyceraldehyde-3-phosphate dehydrogenase, and others involved in SMSincluding proteins involved in transportation of sugar and/or sugaralcohols in particular symporters, preferably galactose-protonsymporter, or exporters of sugar or sugar alcohols, preferably sorbosoneexporter.

In particular, it has now been found that SMS proteins encoded bypolynucleotides having a nucleotide sequence that hybridizes preferablyunder highly stringent conditions to a sequence shown in SEQ ID NO:1play an important role in the biotechnological production of Vitamin C.It has also been found, that by genetically altering the expressionlevel of nucleotides according to the invention in a microorganismcapable of directly producing Vitamin C, such as for exampleGluconobacter, the direct fermentation of Vitamin C by saidmicroorganism can be even greatly improved.

Consequently, the invention relates to a polynucleotide selected fromthe group consisting of:

-   (a) polynucleotides encoding a polypeptide comprising the amino acid    sequence according to SEQ ID NO:2;-   (b) polynucleotides comprising the nucleotide sequence according to    SEQ ID NO:1;-   (c) polynucleotides comprising a nucleotide sequence obtainable by    nucleic acid amplification such as polymerase chain reaction, using    genomic DNA from a microorganism as a template and a primer set    according to SEQ ID NO:3 and SEQ ID NO:4;-   (d) polynucleotides comprising a nucleotide sequence encoding a    fragment or derivative of a polypeptide encoded by a polynucleotide    of any of (a) to (c) wherein in said derivative one or more amino    acid residues are conservatively substituted compared to said    polypeptide, and said fragment or derivative has the activity of a    sugar exporter and/or sugar alcohol exporter, preferably SMS 37    activity;-   (e) polynucleotides the complementary strand of which hybridizes    under stringent conditions to a polynucleotide as defined in any one    of (a) to (d) and which encode a sugar exporter and/or sugar alcohol    exporter, preferably a SMS 37 polypeptide; and-   (f) polynucleotides which are at least 60%, such as 70, 85, 90 or    95% identical to a polynucleotide as defined in any one of (a)    to (d) and which encode a sugar exporter and/or sugar alcohol    exporter, preferably a SMS 37 polypeptide;    or    the complementary strand of such a polynucleotide.

The SMS protein as isolated from Gluconobacter oxydans DSM 17078 shownin SEQ ID NO:2 and described herein was found to be a particularlyuseful SMS protein, since it appeared that it performs a crucialfunction in the direct Vitamin C production in microorganisms, inparticular in bacteria, such as acetic acid bacteria, such asGluconobacter, Acetobacter and Gluconacetobacter. Accordingly, theinvention relates to a polynucleotide encoding a polypeptide accordingto SEQ ID NO:2. This protein may be encoded by a nucleotide sequence asshown in SEQ ID NO:1. The invention therefore also relates topolynucleotides comprising the nucleotide sequence according to SEQ IDNO:1.

The nucleotide and amino acid sequences determined above were used as a“query sequence” to perform a search with Blast2 program (version 2 orBLAST from National Center for Biotechnology [NCBI] against the databasePRO SW-SwissProt (full release plus incremental updates). From thesearches, the SMS 37 polynucleotide according to SEQ ID NO:1 wasannotated as encoding a protein having galactose-proton symporteractivity.

Surprisingly, it has now been furthermore found out that the proteinencoded by the SMS 37 polynucleotide according to SEQ ID NO:1 isinvolved in the export of sugars and/or sugar alcohols, in particularsorbosone. In this connection, “export” means the active transport of arespective compound from the cytoplasm into the periplasm orextracellular environment.

A nucleic acid according to the invention may be obtained by nucleicacid amplification using cDNA, mRNA or alternatively, genomic DNA, as atemplate and appropriate oligonucleotide primers such as the nucleotideprimers according to SEQ ID NO:3 and SEQ ID NO:4 according to standardPCR amplification techniques. The nucleic acid thus amplified may becloned into an appropriate vector and characterized by DNA sequenceanalysis.

The template for the reaction may be cDNA obtained by reversetranscription of mRNA prepared from strains known or suspected tocomprise a polynucleotide according to the invention. The PCR productmay be subcloned and sequenced to ensure that the amplified sequencesrepresent the sequences of a new nucleic acid sequence as describedherein, or a functional equivalent thereof.

The PCR fragment may then be used to isolate a full length cDNA clone bya variety of known methods. For example, the amplified fragment may belabeled and used to screen a bacteriophage or cosmid cDNA library.Alternatively, the labeled fragment may be used to screen a genomiclibrary.

Accordingly, the invention relates to polynucleotides comprising anucleotide sequence obtainable by nucleic acid amplification such aspolymerase chain reaction, using DNA such as genomic DNA from amicroorganism as a template and a primer set according to SEQ ID NO:3and SEQ ID NO:4.

The invention also relates to polynucleotides comprising a nucleotidesequence encoding a fragment or derivative of a polypeptide encoded by apolynucleotide as described herein wherein in said derivative one ormore amino acid residues are conservatively substituted compared to saidpolypeptide, and said fragment or derivative has the activity of a SMSpolypeptide, preferably a SMS 37 polypeptide.

The invention also relates to polynucleotides the complementary strandof which hybridizes under stringent conditions to a polynucleotide asdefined herein and which encode a SMS polypeptide, preferably a SMS 37polypeptide.

The invention also relates to polynucleotides which are at least 60%identical to a polynucleotide as defined herein and which encode a SMSpolypeptide; and the invention also relates to polynucleotides being thecomplementary strand of a polynucleotide as defined herein above.

The invention also relates to primers, probes and fragments that may beused to amplify or detect a DNA according to the invention and toidentify related species or families of microorganisms also carryingsuch genes.

The present invention also relates to vectors which includepolynucleotides of the invention and microorganisms which aregenetically engineered with the polynucleotides or said vectors.

The invention also relates to processes for producing microorganismscapable of expressing a polypeptide encoded by the above definedpolynucleotide and a polypeptide encoded by a polynucleotide as definedabove.

The invention also relates to microorganisms wherein the activity of aSMS polypeptide, preferably a SMS 37 polypeptide, is enhanced and/orimproved so that the yield of Vitamin C which is directly produced fromD-sorbitol or L-sorbose is increased. This may be accomplished, forexample, by transferring a polynucleotide according to the inventioninto a recombinant or non-recombinant microorganism that may or may notcontain an endogenous equivalent of the SMS 37 gene.

The skilled person will know how to enhance and/or improve the activityof a SMS protein, preferably a SMS 37 protein. Such may be for instanceaccomplished by either genetically modifying the host organism in such away that it produces more or more stable copies of the SMS protein,preferably the SMS 37 protein, than the wild type organism or byincreasing the specific activity of the SMS protein, preferably the SMS37 protein.

In the following description, procedures are detailed to achieve thisgoal, i.e. the increase in the yield and/or production of Vitamin Cwhich is which is directly produced from D-sorbitol or L-sorbose byincreasing the activity of a SMS 37 protein. These procedures applymutatis mutandis for other SMS proteins.

Modifications in order to have the organism produce more copies of theSMS 37 gene, i.e. overexpressing the gene, and/or protein may includethe use of a strong promoter, or the mutation (e.g. insertion, deletionor point mutation) of (parts of) the SMS 37 gene or its regulatoryelements. It may also involve the insertion of multiple copies of thegene into a suitable microorganism. An increase in the specific activityof an SMS 37 protein may also be accomplished by methods known in theart. Such methods may include the mutation (e.g. insertion, deletion orpoint mutation) of (parts of) the SMS 37 gene. A gene is said to be“overexpressed” if the level of transcription of said gene is enhancedin comparison to the wild type gene. This may be measured by forinstance Northern blot analysis quantifying the amount of mRNA as anindication for gene expression. As used herein, a gene is overexpressedif the amount of generated mRNA is increased by at least 1%, 2%, 5% 10%,25%, 50%, 75%, 100%, 200% or even more than 500%, compared to the amountof mRNA generated from a wild-type gene.

Also known in the art are methods of increasing the activity of a givenprotein by contacting the SMS 37 protein with specific enhancers orother substances that specifically interact with the SMS 37 protein. Inorder to identify such specific enhancers, the SMS 37 protein may beexpressed and tested for activity in the presence of compounds suspectedto enhance the activity of the SMS 37 protein. The activity of the SMS37 protein may also be increased by stabilizing the messenger RNAencoding SMS 37. Such methods are also known in the art, see forexample, in Sambrook et al., 1989, Molecular Cloning, A LaboratoryManual, Cold Spring Harbor Press, N.Y.; and Ausubel et al. (eds.), 1995,Current Protocols in Molecular Biology, (John Wiley & Sons, N.Y.).

The invention may be performed in/with any microorganism carrying a SMS37 gene or equivalent or homologue thereof. Suitable microorganisms maybe selected from the group consisting of yeast, algae and bacteria,either as wild type strains, mutant strains derived by classicmutagenesis and selection methods or as recombinant strains. Examples ofsuch yeast may be, e.g., Candida, Saccharomyces, Zygosaccharomyces,Schizosaccharomyces, or Kluyveromyces. An example of such algae may be,e.g., Chlorella. Examples of such bacteria may be, e.g., Gluconobacter,Acetobacter, Gluconacetobacter, Ketogulonicigenium, Pantoea,Pseudomonas, such as, e.g., Pseudomonas putida, and Escherichia, suchas, e.g., Escherichia coli. Preferred are Gluconobacter or Acetobacteraceti, such as for instance G. oxydans, G. cerinus, G. frateurii, A.aceti subsp. xylinum or A. aceti subsp. orleanus, preferably G. oxydansDSM 17078. Gluconobacter oxydans DSM 17078 (formerly known asGluconobacter oxydans N44-1) has been deposited at Deutsche Sammlung vonMikroorganismen und Zellkulturen (DSMZ), Mascheroder Weg 1B, D-38124Braunschweig, Germany according to the Budapest Treaty on 26. January2005.

Microorganisms which can be used for the present invention may bepublicly available from different sources, e.g., Deutsche Sammlung vonMikroorganismen und Zellkulturen (DSMZ), Mascheroder Weg 1B, D-38124Braunschweig, Germany, American Type Culture Collection (ATCC), P.O. Box1549, Manassas, Va. 20108 USA or Culture Collection Division, NITEBiological Resource Center, 2-5-8, Kazusakamatari, Kisarazu-shi, Chiba,292-0818, Japan (formerly: Institute for Fermentation, Osaka (IFO),17-85, Juso-honmachi 2-chome, Yodogawa-ku, Osaka 532-8686, Japan).Examples of preferred bacteria deposited with IFO are for instanceGluconobacter oxydans (formerly known as G. melanogenus) IFO 3293,Gluconobacter oxydans (formerly known as G. melanogenus) IFO 3292,Gluconobacter oxydans (formerly known as G. rubiginosus) IFO 3244,Gluconobacter frateurii (formerly known as G. industrius) IFO 3260,Gluconobacter cerinus IFO 3266, Gluconobacter oxydans IFO 3287, andAcetobacter aceti subsp. orleanus IFO 3259, which were all deposited onApr. 5, 1954; Acetobacter aceti subsp. xylinum IFO 13693 deposited onOct. 22, 1975, and Acetobacter aceti subsp. xylinum IFO 13773 depositedon Dec. 8, 1977. Strain Acetobacter sp. ATCC 15164, which is also anexample of a preferred bacterium, was deposited with ATCC. StrainGluconobacter oxydans (formerly known as G. melanogenus) N 44-1 asanother example of a preferred bacterium is a derivative of the strainIFO 3293 and is described in Sugisawa et al., Agric. Biol. Chem. 54:1201-1209, 1990.

A microorganism as of the present invention may carry furthermodifications either on the DNA or protein level (see above), as long assuch modification has a direct impact on the yield, production and/orefficiency of the direct production of Vitamin C from substrates likee.g. D-sorbitol or L-sorbose. Such further modifications may forinstance affect other genes encoding SMS proteins as described above, inparticular genes encoding membrane-bound L-sorbosone dehydrogenases,such as L-sorbosone dehydrogenase SNDHai, or membrane-bound PQQ boundD-sorbitol dehydrogenases. Methods of performing such modifications areknown in the art, with some examples further described herein. For theuse of SNDHai for direct production of Vitamin C as well as thenucleotide and amino acid sequence thereof we refer to WO 2005/017159which is incorporated herein by reference. Furthermore, suchmodification may for instance affect genes involved in themetabolization of D-sorbitol and/or L-sorbose, such as e.g. the gene ora homologue thereof as shown in SEQ ID NO:9, which acts as a repressorof SMS 37 gene, in particular a modification leading to a reduced orabolished activity of said repressor as e.g. according to SEQ ID NO:9.

The skilled person will know how to reduce or abolish the activity ofsaid repressor, preferably a protein according to SEQ ID NO:10. Such maybe for instance accomplished by either genetically modifying the hostorganism in such a way that it produces less or no copies of saidrepressor, preferably protein according to SEQ ID NO:10, than the wildtype organism or by decreasing or abolishing the specific activity ofsaid repressor, preferably the protein according to SEQ ID NO:10.

Modifications in order to have the organism produce less or no copies ofsuch a repressor gene, preferably a gene according to SEQ ID NO:9,and/or protein according to SEQ ID NO:10 may include the use of a weakpromoter, or the mutation (e.g. insertion, deletion or point mutation)of (parts of) the gene according to SEQ ID NO:9 or its regulatoryelements. Decreasing or abolishing the specific activity of a proteinaccording to SEQ ID NO:10 may also be accomplished by methods known inthe art. Such methods may include the mutation (e.g. insertion, deletionor point mutation) of (parts of) a gene according to SEQ ID NO:9. Thismay for instance affect the interaction with DNA that is mediated by theN-terminal region of a protein according to SEQ ID NO:10 or interactionwith other effector molecules.

Also known in the art are methods of reducing or abolishing the activityof a given protein by contacting the protein according to SEQ ID NO:10with specific inhibitors or other substances that specifically interactwith said protein. In order to identify such specific inhibitors, saidprotein may be expressed and tested for activity in the presence ofcompounds suspected to inhibit the activity of said protein. Potentialinhibiting compounds may for instance be monoclonal or polyclonalantibodies against said protein. Such antibodies may be obtained byroutine immunization protocols of suitable laboratory animals.

In accordance with a further object of the present invention there isprovided the use of a polynucleotide as defined above or a microorganismwhich is genetically engineered using such polynucleotides in theproduction of Vitamin C.

The invention also relates to processes for the expression of endogenousgenes in a microorganism, to processes for the production ofpolypeptides as defined above in a microorganism and to processes forthe production of microorganisms capable of producing Vitamin C. Allthese processes may comprise the step of altering a microorganism,wherein “altering” as used herein encompasses the process for“genetically altering” or “altering the composition of the cell culturemedia and/or methods used for culturing” in such a way that the yieldand/or productivity of the fermentation product can be improved comparedto the wild-type organism. As used herein, “improved yield of Vitamin C”means an increase of at least 5%, 10%, 25%, 30%, 40%, 50%, 75%, 100%,200% or even more than 500%, compared to a wild-type microorganism, i.e.a microorganism which is not genetically altered.

The term “genetically engineered” or “genetically altered” means thescientific alteration of the structure of genetic material in a livingorganism. It involves the production and use of recombinant DNA. More inparticular it is used to delineate the genetically engineered ormodified organism from the naturally occurring organism. Geneticengineering may be done by a number of techniques known in the art, suchas e.g. gene replacement, gene amplification, gene disruption,transfection, transformation using plasmids, viruses, or other vectors.A genetically modified organism, e.g. genetically modifiedmicroorganism, is also often referred to as a recombinant organism, e.g.recombinant microorganism.

Thus, the present invention may include either (1) a recombinantmicroorganism carrying in addition to its natural gene, e.g. the geneencoding SMS 37, further copies of said gene introduced by geneticengineering of said microorganism by techniques known in the art andsuch as exemplified herein, or (2) a recombinant microorganismgenetically engineered as above but which does not naturally carry sucha gene as e.g. the gene encoding SMS 37. Preferably, a recombinantmicroorganism as of the present invention is modified such that itcarries more copies of DNA encoding SMS 37 as the wildtypemicroorganism, in particular as a result of transformation with aplasmid carrying one or more copies of a DNA encoding SMS 37 orintegration of such DNA encoding SMS 37 into its genome.

In accordance with still another aspect of the invention there isprovided a process for the production of Vitamin C by directfermentation.

In particular, the present invention provides a process for the directproduction of Vitamin C comprising converting a substrate into VitaminC.

Several substrates may be used as a carbon source in a process of thepresent invention, i.e. a process for direct conversion of a givensubstrate into Vitamin C such as e.g. mentioned above. Particularlysuited carbon sources are those that are easily obtainable from theD-glucose or D-sorbitol metabolization pathway such as, for example,D-glucose, D-sorbitol, L-sorbose, L-sorbosone, 2-keto-L-gulonate,D-gluconate, 2-keto-D-gluconate or 2,5-diketo-gluconate. Preferably, thesubstrate is selected from for instance D-glucose, D-sorbitol, L-sorboseor L-sorbosone, more preferably from D-glucose, D-sorbitol or L-sorbose,and most preferably from D-sorbitol, L-sorbose or L-sorbosone. The term“substrate” and “production substrate” in connection with the aboveprocess using a microorganism is used interchangeably herein.

A medium as used herein for the above process using a microorganism maybe any suitable medium for the production of Vitamin C. Typically, themedium is an aqueous medium comprising for instance salts, substrate(s),and a certain pH. The medium in which the substrate is converted intoVitamin C is also referred to as the production medium.

“Fermentation” or “production” or “fermentation process” as used hereinmay be the use of growing cells using media, conditions and proceduresknown to the skilled person, or the use of non-growing so-called restingcells, after they have been cultivated by using media, conditions andprocedures known to the skilled person, under appropriate conditions forthe conversion of suitable substrates into desired products such asVitamin C. Preferably, resting cells are used for the production ofVitamin C.

The term “direct fermentation”, “direct production”, “direct conversion”and the like is intended to mean that a microorganism is capable of theconversion of a certain substrate into the specified product by means ofone or more biological conversion steps, without the need of anyadditional chemical conversion step. For instance, the term “directconversion of D-sorbitol into Vitamin C” is intended to describe aprocess wherein a microorganism is producing Vitamin C and whereinD-sorbitol is offered as a carbon source without the need of anintermediate chemical conversion step. A single microorganism capable ofdirectly fermenting Vitamin C is preferred. Said microorganism iscultured under conditions which allow such conversion from the substrateas defined above.

In connection with the above process using a microorganism it isunderstood that the above-mentioned microorganisms also include synonymsor basonyms of such species having the same physiological properties, asdefined by the International Code of Nomenclature of Prokaryotes. Thenomenclature of the microorganisms as used herein is the one officiallyaccepted (at the filing date of the priority application) by theInternational Committee on Systematics of Prokaryotes and theBacteriology and Applied Microbiology Division of the InternationalUnion of Microbiological Societies, and published by its officialpublication vehicle International Journal of Systematic and EvolutionaryMicrobiology (IJSEM). A particular reference is made to Urbance et al.,IJSEM (2001) vol 51:1059-1070, with a corrective notification on IJSEM(2001) vol 51:1231-1233, describing the taxonomically reclassificationof G. oxydans DSM 4025 as Ketogulonicigenium vulgare.

As used herein, resting cells refer to cells of a microorganism whichare for instance viable but not actively growing, or which are growingat low specific growth rates, for instance, growth rates that are lowerthan 0.02 h⁻¹, preferably lower than 0.01 h⁻¹. Cells which show theabove growth rates are said to be in a “resting cell mode”.

The process of the present invention as above using a microorganism maybe performed in different steps or phases: preferably, the microorganismis cultured in a first step (also referred to as step (a) or growthphase) under conditions which enable growth. This phase is terminated bychanging of the conditions such that the growth rate of themicroorganism is reduced leading to resting cells, also referred to asstep (b), followed by the production of Vitamin C from the substrateusing the (b), also referred to as production phase.

Growth and production phase as performed in the above process using amicroorganism may be performed in the same vessel, i.e., only onevessel, or in two or more different vessels, with an optional cellseparation step between the two phases. The produced Vitamin C can berecovered from the cells by any suitable means. Recovering means forinstance that the produced Vitamin C may be separated from theproduction medium. Optionally, the thus produced Vitamin C may befurther processed.

For the purpose of the present invention relating to the above processusing a microorganism, the terms “growth phase”, “growing step”, “growthstep” and “growth period” are used interchangeably herein. The sameapplies for the terms “production phase”, “production step”, “productionperiod”.

One way of performing the above process using a microorganism as of thepresent invention may be a process wherein the microorganism is grown ina first vessel, the so-called growth vessel, as a source for the restingcells, and at least part of the cells are transferred to a secondvessel, the so-called production vessel. The conditions in theproduction vessel may be such that the cells transferred from the growthvessel become resting cells as defined above. Vitamin C is produced inthe second vessel and recovered therefrom.

In connection with the above process using a microorganism, in oneaspect, the growing step can be performed in an aqueous medium, i.e. thegrowth medium, supplemented with appropriate nutrients for growth underaerobic conditions. The cultivation may be conducted, for instance, inbatch, fed-batch, semi-continuous or continuous mode. The cultivationperiod may vary depending on for instance the host, pH, temperature andnutrient medium to be used, and may be for instance about 10 h to about10 days, preferably about 1 to about 10 days, more preferably about 1 toabout 5 days when run in batch or fed-batch mode, depending on themicroorganism. If the cells are grown in continuous mode, the residencetime may be for instance from about 2 to about 100 h, preferably fromabout 2 to about 50 h, depending on the microorganism. If themicroorganism is selected from bacteria, the cultivation may beconducted for instance at a pH of about 3.0 to about 9.0, preferablyabout 4.0 to about 9.0, more preferably about 4.0 to about 8.0, evenmore preferably about 5.0 to about 8.0. If algae or yeast are used, thecultivation may be conducted, for instance, at a pH below about 7.0,preferably below about 6.0, more preferably below about 5.5, and mostpreferably below about 5.0. A suitable temperature range for carryingout the cultivation using bacteria may be for instance from about 13° C.to about 40° C., preferably from about 18° C. to about 37° C., morepreferably from about 13° C. to about 36° C., and most preferably fromabout 18° C. to about 33° C. If algae or yeast are used, a suitabletemperature range for carrying out the cultivation may be for instancefrom about 15° C. to about 40° C., preferably from about 20° C. to about45° C., more preferably from about 25° C. to about 40° C., even morepreferably from about 25° C. to about 38° C., and most preferably fromabout 30° C. to about 38° C. The culture medium for growth usually maycontain such nutrients as assimilable carbon sources, e.g., glycerol,D-mannitol, D-sorbitol, L-sorbose, erythritol, ribitol, xylitol,arabitol, inositol, dulcitol, D-ribose, D-fructose, D-glucose, sucrose,and ethanol, preferably L-sorbose, D-glucose, D-sorbitol, D-mannitol,glycerol and ethanol; and digestible nitrogen sources such as organicsubstances, e.g., peptone, yeast extract and amino acids. The media maybe with or without urea and/or corn steep liquor and/or baker's yeast.Various inorganic substances may also be used as nitrogen sources, e.g.,nitrates and ammonium salts. Furthermore, the growth medium, usually maycontain inorganic salts, e.g., magnesium sulfate, manganese sulfate,potassium phosphate, and calcium carbonate. Cells obtained using theprocedures described above can then be further incubated at essentiallythe same modes, temperature and pH conditions as described above, in thepresence of substrates such as D-sorbitol, L-sorbose, or D-glucose, insuch a way that they convert these substrates directly into Vitamin C.Incubation can be done in a nitrogen-rich medium, containing, forexample, organic nitrogen sources, e.g., peptone, yeast extract, baker'syeast, urea, amino acids, and corn steep liquor, or inorganic nitrogensources, e.g., nitrates and ammonium salts, in which case cells will beable to further grow while producing Vitamin C. Alternatively,incubation can be done in a nitrogen-poor medium, in which case cellswill not grow substantially, and will be in a resting cell mode, orbiotransformation mode. In all cases, the incubation medium may alsocontain inorganic salts, e.g., magnesium sulfate, manganese sulfate,potassium phosphate, and calcium chloride.

In connection with the above process using a microorganism, in thegrowth phase the specific growth rates are for instance at least 0.02h⁻¹. For cells growing in batch, fed-batch or semi-continuous mode, thegrowth rate depends on for instance the composition of the growthmedium, pH, temperature, and the like. In general, the growth rates maybe for instance in a range from about 0.05 to about 0.2 h⁻¹, preferablyfrom about 0.06 to about 0.15 h⁻¹, and most preferably from about 0.07to about 0.13 h⁻¹.

In another aspect of the above process using a microorganism, restingcells may be provided by cultivation of the respective microorganism onagar plates thus serving as growth vessel, using essentially the sameconditions, e.g., cultivation period, pH, temperature, nutrient mediumas described above, with the addition of agar agar.

In connection with the above process using a microorganism, if thegrowth and production phase are performed in two separate vessels, thenthe cells from the growth phase may be harvested or concentrated andtransferred to a second vessel, the so-called production vessel. Thisvessel may contain an aqueous medium supplemented with any applicableproduction substrate that can be converted to Vitamin C by the cells.Cells from the growth vessel can be harvested or concentrated by anysuitable operation, such as for instance centrifugation, membranecrossflow ultrafiltration or microfiltration, filtration, decantation,flocculation. The cells thus obtained may also be transferred to theproduction vessel in the form of the original broth from the growthvessel, without being harvested, concentrated or washed, i.e. in theform of a cell suspension. In a preferred embodiment, the cells aretransferred from the growth vessel to the production vessel in the formof a cell suspension without any washing or isolating step in-between.

Thus, in a preferred embodiment of the above process using amicroorganism step (a) and (c) of the process of the present inventionas described above are not separated by any washing and/or separationstep.

In connection with the above process using a microorganism, if thegrowth and production phase are performed in the same vessel, cells maybe grown under appropriate conditions to the desired cell densityfollowed by a replacement of the growth medium with the productionmedium containing the production substrate. Such replacement may be, forinstance, the feeding of production medium to the vessel at the sametime and rate as the withdrawal or harvesting of supernatant from thevessel. To keep the resting cells in the vessel, operations for cellrecycling or retention may be used, such as for instance cell recyclingsteps. Such recycling steps, for instance, include but are not limitedto methods using centrifuges, filters, membrane crossflowmicrofiltration of ultrafiltration steps, membrane reactors,flocculation, or cell immobilization in appropriate porous, non-porousor polymeric matrixes. After a transition phase, the vessel is broughtto process conditions under which the cells are in a resting cell modeas defined above, and the production substrate is efficiently convertedinto Vitamin C.

The aqueous medium in the production vessel as used for the productionstep in connection with the above process using a microorganism,hereinafter called production medium, may contain only the productionsubstrate(s) to be converted into Vitamin C, or may contain for instanceadditional inorganic salts, e.g., sodium chloride, calcium chloride,magnesium sulfate, manganese sulfate, potassium phosphate, calciumphosphate, and calcium carbonate. The production medium may also containdigestible nitrogen sources such as for instance organic substances,e.g., peptone, yeast extract, urea, amino acids, and corn steep liquor,and inorganic substances, e.g. ammonia, ammonium sulfate, and sodiumnitrate, at such concentrations that the cells are kept in a restingcell mode as defined above. The medium may be with or without ureaand/or corn steep liquor and/or baker's yeast. The production step maybe conducted for instance in batch, fed-batch, semi-continuous orcontinuous mode. In case of fed-batch, semi-continuous or continuousmode, both cells from the growth vessel and production medium can be fedcontinuously or intermittently to the production vessel at appropriatefeed rates. Alternatively, only production medium may be fedcontinuously or intermittently to the production vessel, while the cellscoming from the growth vessel are transferred at once to the productionvessel. The cells coming from the growth vessel may be used as a cellsuspension within the production vessel or may be used as for instanceflocculated or immobilized cells in any solid phase such as porous orpolymeric matrixes. The production period, defined as the period elapsedbetween the entrance of the substrate into the production vessel and theharvest of the supernatant containing Vitamin C, the so-called harveststream, can vary depending for instance on the kind and concentration ofcells, pH, temperature and nutrient medium to be used, and is preferablyabout 2 to about 100 h. The pH and temperature can be different from thepH and temperature of the growth step, but is essentially the same asfor the growth step.

In a preferred embodiment of the above process using a microorganism,the production step is conducted in continuous mode, meaning that afirst feed stream containing the cells from the growth vessel and asecond feed stream containing the substrate is fed continuously orintermittently to the production vessel. The first stream may eithercontain only the cells isolated/separated from the growth medium or acell suspension, coming directly from the growth step, i.e. cellssuspended in growth medium, without any intermediate step of cellseparation, washing and/or isolating. The second feed stream as hereindefined may include all other feed streams necessary for the operationof the production step, e.g. the production medium comprising thesubstrate in the form of one or several different streams, water fordilution, and base for pH control.

In connection with the above process using a microorganism, when bothstreams are fed continuously, the ratio of the feed rate of the firststream to feed rate of the second stream may vary between about 0.01 andabout 10, preferably between about 0.01 and about 5, most preferablybetween about 0.02 and about 2. This ratio is dependent on theconcentration of cells and substrate in the first and second stream,respectively.

Another way of performing the process as above using a microorganism ofthe present invention may be a process using a certain cell density ofresting cells in the production vessel. The cell density is measured asabsorbance units (optical density) at 600 nm by methods known to theskilled person. In a preferred embodiment, the cell density in theproduction step is at least about 10, more preferably between about 10and about 200, even more preferably between about 15 and about 200, evenmore preferably between about 15 to about 120, and most preferablybetween about 20 and about 120.

In connection with the above process using a microorganism, in order tokeep the cells in the production vessel at the desired cell densityduring the production phase as performed, for instance, in continuous orsemi-continuous mode, any means known in the art may be used, such asfor instance cell recycling by centrifugation, filtration, membranecrossflow ultrafiltration of microfiltration, decantation, flocculation,cell retention in the vessel by membrane devices or cell immobilization.Further, in case the production step is performed in continuous orsemi-continuous mode and cells are continuously or intermittently fedfrom the growth vessel, the cell density in the production vessel may bekept at a constant level by, for instance, harvesting an amount of cellsfrom the production vessel corresponding to the amount of cells beingfed from the growth vessel.

In connection with the above process using a microorganism, the producedVitamin C contained in the so-called harvest stream isrecovered/harvested from the production vessel. The harvest stream mayinclude, for instance, cell-free or cell-containing aqueous solutioncoming from the production vessel, which contains Vitamin C as a resultof the conversion of production substrate by the resting cells in theproduction vessel. Cells still present in the harvest stream may beseparated from the Vitamin C by any operations known in the art, such asfor instance filtration, centrifugation, decantation, membrane crossflowultrafiltration or microfiltration, tangential flow ultrafiltration ormicrofiltration or dead end filtration. After this cell separationoperation, the harvest stream is essentially free of cells.

In a further aspect, the process of the present invention may becombined with further steps of separation and/or purification of theproduced Vitamin C from other components contained in the harveststream, i.e., so-called downstream processing steps. These steps mayinclude any means known to a skilled person, such as, for instance,concentration, crystallization, precipitation, adsorption, ion exchange,electrodialysis, bipolar membrane electrodialysis and/or reverseosmosis. Vitamin C may be further purified as the free acid form or anyof its known salt forms by means of operations such as for instancetreatment with activated carbon, ion exchange, adsorption and elution,concentration, crystallization, filtration and drying. Specifically, afirst separation of Vitamin C from other components in the harveststream might be performed by any suitable combination or repetition of,for instance, the following methods: two- or three-compartmentelectrodialysis, bipolar membrane electrodialysis, reverse osmosis oradsorption on, for instance, ion exchange resins or non-ionic resins. Ifthe resulting form of Vitamin C is a salt of L-ascorbic acid, conversionof the salt form into the free acid form may be performed by forinstance bipolar membrane electrodialysis, ion exchange, simulatedmoving bed chromatographic techniques, and the like. Combination of thementioned steps, e.g., electrodialysis and bipolar membraneelectrodialysis into one step might be also used as well as combinationof the mentioned steps e.g. several steps of ion exchange by usingsimulated moving bed chromatographic methods. Any of these proceduresalone or in combination constitute a convenient means for isolating andpurifying the product, i.e. Vitamin C. The product thus obtained mayfurther be isolated in a manner such as, e.g. by concentration,crystallization, precipitation, washing and drying of the crystalsand/or further purified by, for instance, treatment with activatedcarbon, ion exchange and/or re-crystallization.

In a preferred embodiment, Vitamin C is purified from the harvest streamby a series of downstream processing steps as described above withouthaving to be transferred to a non-aqueous solution at any time of thisprocessing, i.e. all steps are performed in an aqueous environment. Suchpreferred downstream processing procedure may include for instance theconcentration of the harvest stream coming from the production vessel bymeans of two- or three-compartment electrodialysis, conversion ofVitamin C in its salt form present in the concentrated solution into itsacid form by means of bipolar membrane electrodialysis and/or ionexchange, purification by methods such as for instance treatment withactivated carbon, ion exchange or non-ionic resins, followed by afurther concentration step and crystallization. These crystals can beseparated, washed and dried. If necessary, the crystals may be againre-solubilized in water, treated with activated carbon and/or ionexchange resins and recrystallized. These crystals can then beseparated, washed and dried.

Advantageous embodiments of the invention become evident from thedependent claims. These and other aspects and embodiments of the presentinvention should be apparent to those skilled in the art from theteachings herein.

The sequence of the gene comprising a nucleotide sequence according toSEQ ID NO:1 encoding a SMS 37 protein was determined by sequencing agenomic clone obtained from Gluconobacter oxydans DSM 17078.

The invention also relates to a polynucleotide encoding at least abiologically active fragment or derivative of a SMS 37 polypeptide asshown in SEQ ID NO:2.

As used herein, “biologically active fragment or derivative” means apolypeptide which retains essentially the same biological function oractivity as the polypeptide shown in SEQ ID NO:2. Examples of biologicalactivity may for instance be enzymatic activity, signaling activity orantibody reactivity. The term “same biological function” or “functionalequivalent” as used herein means that the protein has essentially thesame biological activity, e.g. enzymatic, signaling or antibodyreactivity, as a polypeptide shown in SEQ ID NO:2.

The polypeptides and polynucleotides of the present invention arepreferably provided in an isolated form, and preferably are purified tohomogeneity.

The term “isolated” means that the material is removed from its originalenvironment (e.g., the natural environment if it is naturallyoccurring). For example, a naturally-occurring polynucleotide orpolypeptide present in a living microorganism is not isolated, but thesame polynucleotide or polypeptide, separated from some or all of thecoexisting materials in the natural system, is isolated. Suchpolynucleotides could be part of a vector and/or such polynucleotides orpolypeptides could be part of a composition and still be isolated inthat such vector or composition is not part of its natural environment.

An isolated polynucleotide or nucleic acid as used herein may be a DNAor RNA that is not immediately contiguous with both of the codingsequences with which it is immediately contiguous (one on the 5′-end andone on the 3′-end) in the naturally occurring genome of the organismfrom which it is derived. Thus, in one embodiment, a nucleic acidincludes some or all of the 5′-non-coding (e.g., promoter) sequencesthat are immediately contiguous to the coding sequence. The term“isolated polynucleotide” therefore includes, for example, a recombinantDNA that is incorporated into a vector, into an autonomously replicatingplasmid or virus, or into the genomic DNA of a prokaryote or eukaryote,or which exists as a separate molecule (e.g., a cDNA or a genomic DNAfragment produced by PCR or restriction endonuclease treatment)independent of other sequences. It also includes a recombinant DNA thatis part of a hybrid gene encoding an additional polypeptide that issubstantially free of cellular material, viral material, or culturemedium (when produced by recombinant DNA techniques), or chemicalprecursors or other chemicals (when chemically synthesized). Moreover,an “isolated nucleic acid fragment” is a nucleic acid fragment that isnot naturally occurring as a fragment and would not be found in thenatural state.

As used herein, the terms “polynucleotide”, “gene” and “recombinantgene” refer to nucleic acid molecules which may be isolated fromchromosomal DNA, which include an open reading frame encoding a protein,e.g. G. oxydans DSM 17078 STS proteins. A polynucleotide may include apolynucleotide sequence as shown in SEQ ID NO:1 or fragments thereof andregions upstream and downstream of the gene sequences which may include,for example, promoter regions, regulator regions and terminator regionsimportant for the appropriate expression and stabilization of thepolypeptide derived thereof.

A gene may include coding sequences, non-coding sequences such as forinstance untranslated sequences located at the 3′- and 5′-ends of thecoding region of a gene, and regulatory sequences. Moreover, a generefers to an isolated nucleic acid molecule as defined herein. It isfurthermore appreciated by the skilled person that DNA sequencepolymorphisms that lead to changes in the amino acid sequences of SMSproteins may exist within a population, e.g., the Gluconobacter oxydanspopulation. Such genetic polymorphism in the SMS 37 gene may exist amongindividuals within a population due to natural variation or in cellsfrom different populations. Such natural variations can typically resultin 1-5% variance in the nucleotide sequence of the SMS 37 gene. Any andall such nucleotide variations and the resulting amino acid polymorphismin SMS 37 are the result of natural variation and that do not alter thefunctional activity of SMS proteins are intended to be within the scopeof the invention.

As used herein, the terms “polynucleotide” or “nucleic acid molecule”are intended to include DNA molecules (e.g., cDNA or genomic DNA) andRNA molecules (e.g., mRNA) and analogs of the DNA or RNA generated usingnucleotide analogs. The nucleic acid molecule may be single-stranded ordouble-stranded, but preferably is double-stranded DNA. The nucleic acidmay be synthesized using oligonucleotide analogs or derivatives (e.g.,inosine or phosphorothioate nucleotides). Such oligonucleotides may beused, for example, to prepare nucleic acids that have alteredbase-pairing abilities or increased resistance to nucleases.

The sequence information as provided herein should not be so narrowlyconstrued as to require inclusion of erroneously identified bases. Thespecific sequences disclosed herein may be readily used to isolate thecomplete gene from a recombinant or non-recombinant microorganismcapable of converting a given carbon source directly into Vitamin C, inparticular Gluconobacter oxydans, preferably Gluconobacter oxydans DSM17078 which in turn may easily be subjected to further sequence analysesthereby identifying sequencing errors.

Unless otherwise indicated, all nucleotide sequences determined bysequencing a DNA molecule herein were determined using an automated DNAsequencer and all amino acid sequences of polypeptides encoded by DNAmolecules determined herein were predicted by translation of a DNAsequence determined as above. Therefore, as is known in the art for anyDNA sequence determined by this automated approach, any nucleotidesequence determined herein may contain some errors. Nucleotide sequencesdetermined by automation are typically at least about 90% identical,more typically at least about 95% to at least about 99.9% identical tothe actual nucleotide sequence of the sequenced DNA molecule. The actualsequence may be more precisely determined by other approaches includingmanual DNA sequencing methods well known in the art. As is also known inthe art, a single insertion or deletion in a determined nucleotidesequence compared to the actual sequence will cause a frame shift intranslation of the nucleotide sequence such that the predicted aminoacid sequence encoded by a determined nucleotide sequence will becompletely different from the amino acid sequence actually encoded bythe sequenced DNA molecule, beginning at the point of such an insertionor deletion.

The person skilled in the art is capable of identifying such erroneouslyidentified bases and knows how to correct for such errors.

A nucleic acid molecule according to the invention may comprise only aportion or a fragment of the nucleic acid sequence provided by thepresent invention, such as for instance the sequence shown in SEQ IDNO:1, for example a fragment which may be used as a probe or primer suchas for instance SEQ ID NO:3 or SEQ ID NO:4 or a fragment encoding aportion of a protein according to the invention. The nucleotide sequencedetermined from the cloning of the SMS 37 gene allows for the generationof probes and primers designed for use in identifying and/or cloningother SMS 37 family members, as well as SMS 37 homologues from otherspecies. The probe/primer typically comprises substantially purifiedoligonucleotides which typically comprises a region of nucleotidesequence that hybridizes preferably under highly stringent conditions toat least about 12 or 15, preferably about 18 or 20, more preferablyabout 22 or 25, even more preferably about 30, 35, 40, 45, 50, 55, 60,65, or 75 or more consecutive nucleotides of a nucleotide sequence shownin SEQ ID NO:1 or a fragment or derivative thereof.

A nucleic acid molecule encompassing all or a portion of the nucleicacid sequence of SEQ ID NO:1 may be also isolated by the polymerasechain reaction (PCR) using synthetic oligonucleotide primers designedbased upon the sequence information contained herein.

A nucleic acid of the invention may be amplified using cDNA, mRNA oralternatively, genomic DNA, as a template and appropriateoligonucleotide primers according to standard PCR amplificationtechniques. The nucleic acid thus amplified may be cloned into anappropriate vector and characterized by DNA sequence analysis.

Fragments of a polynucleotide according to the invention may alsocomprise polynucleotides not encoding functional polypeptides. Suchpolynucleotides may function as probes or primers for a PCR reaction.

Nucleic acids according to the invention irrespective of whether theyencode functional or non-functional polypeptides, may be used ashybridization probes or polymerase chain reaction (PCR) primers. Uses ofthe nucleic acid molecules of the present invention that do not encode apolypeptide having a SMS 37 activity include, inter alia, (1) isolatingthe gene encoding the protein of the present invention, or allelicvariants thereof from a cDNA library, e.g., from other organisms thanGluconobacter oxydans and (2) Northern blot analysis for detectingexpression of mRNA of said protein in specific cells or (3) use inenhancing and/or improving the function or activity of homologous SMS 37genes in said other organisms.

Probes based on the nucleotide sequences provided herein may be used todetect transcripts or genomic sequences encoding the same or homologousproteins for instance in other organisms. Nucleic acid moleculescorresponding to natural variants and non-G. oxydans homologues of theG. oxydans SMS 37 DNA of the invention which are also embraced by thepresent invention may be isolated based on their homology to the G.oxydans SMS 37 nucleic acid disclosed herein using the G. oxydans DNA,or a portion thereof, as a hybridization probe according to standardhybridization techniques, preferably under highly stringenthybridization conditions.

In preferred embodiments, the probe further comprises a label groupattached thereto, e.g., the label group can be a radioisotope, afluorescent compound, an enzyme, or an enzyme cofactor.

Homologous gene sequences may be isolated, for example, by performingPCR using two degenerate oligonucleotide primer pools designed on thebasis of nucleotide sequences as taught herein.

The template for the reaction may be cDNA obtained by reversetranscription of mRNA prepared from strains known or suspected toexpress a polynucleotide according to the invention. The PCR product maybe subcloned and sequenced to ensure that the amplified sequencesrepresent the sequences of a new nucleic acid sequence as describedherein, or a functional equivalent thereof.

The PCR fragment may then be used to isolate a full length cDNA clone bya variety of known methods. For example, the amplified fragment may belabeled and used to screen a bacteriophage or cosmid cDNA library.Alternatively, the labeled fragment may be used to screen a genomiclibrary.

PCR technology can also be used to isolate full-length cDNA sequencesfrom other organisms. For example, RNA may be isolated, followingstandard procedures, from an appropriate cellular or tissue source. Areverse transcription reaction may be performed on the RNA using anoligonucleotide primer specific for the most 5′-end of the amplifiedfragment for the priming of first strand synthesis.

The resulting RNA/DNA hybrid may then be “tailed” (e.g., with guanines)using a standard terminal transferase reaction, the hybrid may bedigested with RNaseH, and second strand synthesis may then be primed(e.g., with a poly-C primer). Thus, cDNA sequences upstream of theamplified fragment may easily be isolated. For a review of usefulcloning strategies, see e.g., Sambrook et al., supra; and Ausubel etal., supra.

Also, nucleic acids encoding other SMS 37 family members, which thushave a nucleotide sequence that differs from a nucleotide sequenceaccording to SEQ ID NO:1, are within the scope of the invention.Moreover, nucleic acids encoding SMS 37 proteins from different specieswhich thus may have a nucleotide sequence which differs from anucleotide sequence shown in SEQ ID NO:1 are within the scope of theinvention.

The invention also relates to an isolated polynucleotide hybridisableunder stringent conditions, preferably under highly stringentconditions, to a polynucleotide as of the present invention, such as forinstance a polynucleotide shown in SEQ ID NO:1. Advantageously, suchpolynucleotide may be obtained from a microorganism capable ofconverting a given carbon source directly into Vitamin C, in particularGluconobacter oxydans, preferably Gluconobacter oxydans DSM 17078.

As used herein, the term “hybridizing” is intended to describeconditions for hybridization and washing under which nucleotidesequences at least about 50%, at least about 60%, at least about 70%,more preferably at least about 80%, even more preferably at least about85% to 90%, most preferably at least 95% homologous to each othertypically remain hybridized to each other.

In one embodiment, a nucleic acid of the invention is at least 40%, 45%,50%, 55%, 60%, 65%, 70%, 75%, 80%, 85%, 90%, 91%, 92%, 93%, 94%, 95%,96%, 97%, 98%, 99%, or more homologous to a nucleic acid sequence shownin SEQ ID NO:1 or the complement thereof.

A preferred, non-limiting example of stringent hybridization conditionsare hybridization in 6× sodium chloride/sodium citrate (SSC) at about45° C., followed by one or more washes in 1×SSC, 0.1% SDS at 50° C.,preferably at 55° C., more preferably at 60° C. and even more preferablyat 65° C.

Highly stringent conditions include incubations at 42° C. for a periodof several days, such as 2-4 days, using a labeled DNA probe, such as adigoxigenin (DIG)-labeled DNA probe, followed by one or more washes in2×SSC, 0.1% SDS at room temperature and one or more washes in 0.5×SSC,0.1% SDS or 0.1×SSC, 0.1% SDS at 65-68° C. In particular, highlystringent conditions include, for example, 2 h to 4 days incubation at42° C. using a DIG-labeled DNA probe (prepared by e.g. using a DIGlabeling system; Roche Diagnostics GmbH, 68298 Mannheim, Germany) in asolution such as DigEasyHyb solution (Roche Diagnostics GmbH) with orwithout 100 μg/ml salmon sperm DNA, or a solution comprising 50%formamide, 5×SSC (150 mM NaCl, 15 mM trisodium citrate), 0.02% sodiumdodecyl sulfate, 0.1% N-lauroylsarcosine, and 2% blocking reagent (RocheDiagnostics GmbH), followed by washing the filters twice for 5 to 15minutes in 2×SSC and 0.1% SDS at room temperature and then washing twicefor 15-30 minutes in 0.5×SSC and 0.1% SDS or 0.1×SSC and 0.1% SDS at65-68° C.

Preferably, an isolated nucleic acid molecule of the invention thathybridizes under preferably highly stringent conditions to a nucleotidesequence of the invention corresponds to a naturally-occurring nucleicacid molecule. As used herein, a “naturally-occurring”nucleic acidmolecule refers to an RNA or DNA molecule having a nucleotide sequencethat occurs in nature (e.g., encodes a natural protein). In oneembodiment, the nucleic acid encodes a natural G. oxydans SMS 37protein.

The skilled artisan will know which conditions to apply for stringentand highly stringent hybridization conditions. Additional guidanceregarding such conditions is readily available in the art, for example,in Sambrook et al., 1989, Molecular Cloning, A Laboratory Manual, ColdSpring Harbor Press, N.Y.; and Ausubel et al. (eds.), 1995, CurrentProtocols in Molecular Biology, (John Wiley & Sons, N.Y.). Of course, apolynucleotide which hybridizes only to a poly (A) sequence (such as the3′-terminal poly (A) tract of mRNAs), or to a complementary stretch of T(or U) residues, would not be included in a polynucleotide of theinvention used to specifically hybridize to a portion of a nucleic acidof the invention, since such a polynucleotide would hybridize to anynucleic acid molecule containing a poly (A) stretch or the complementthereof (e.g., practically any double-stranded cDNA clone).

In a typical approach, genomic DNA or cDNA libraries constructed fromother organisms, e.g. microorganisms capable of converting a givencarbon source directly into Vitamin C, in particular other Gluconobacterspecies may be screened.

For example, Gluconobacter strains may be screened for homologouspolynucleotides by Southern and/or Northern blot analysis. Upondetection of transcripts homologous to polynucleotides according to theinvention, DNA libraries may be constructed from RNA isolated from theappropriate strain, utilizing standard techniques well known to those ofskill in the art. Alternatively, a total genomic DNA library may bescreened using a probe hybridisable to a polynucleotide according to theinvention.

A nucleic acid molecule of the present invention, such as for instance anucleic acid molecule shown in SEQ ID NO:1 or a fragment or derivativethereof, may be isolated using standard molecular biology techniques andthe sequence information provided herein. For example, using all orportion of the nucleic acid sequence shown in SEQ ID NO:1 as ahybridization probe, nucleic acid molecules according to the inventionmay be isolated using standard hybridization and cloning techniques(e.g., as described in Sambrook, J., Fritsh, E. F., and Maniatis, T.Molecular Cloning: A Laboratory Manual. 2nd, ed., Cold Spring HarborLaboratory, Cold Spring Harbor Laboratory Press, Cold Spring Harbor,N.Y., 1989).

Furthermore, oligonucleotides corresponding to or hybridisable tonucleotide sequences according to the invention may be prepared bystandard synthetic techniques, e.g., using an automated DNA synthesizer.

The terms “homology” or “percent identity” are used interchangeablyherein. For the purpose of this invention, it is defined here that inorder to determine the percent identity of two amino acid sequences orof two nucleic acid sequences, the sequences are aligned for optimalcomparison purposes (e.g., gaps may be introduced in the sequence of afirst amino acid or nucleic acid sequence for optimal alignment with asecond amino or nucleic acid sequence). The amino acid residues ornucleotides at corresponding amino acid positions or nucleotidepositions are then compared. When a position in the first sequence isoccupied by the same amino acid residue or nucleotide as thecorresponding position in the second sequence, then the molecules areidentical at that position. The percent identity between the twosequences is a function of the number of identical positions shared bythe sequences (i.e., % identity=number of identical positions/totalnumber of positions (i.e., overlapping positions)×100). Preferably, thetwo sequences are the same length.

The skilled person will be aware of the fact that several differentcomputer programs are available to determine the homology between twosequences. For instance, a comparison of sequences and determination ofpercent identity between two sequences may be accomplished using amathematical algorithm. In a preferred embodiment, the percent identitybetween two amino acid sequences is determined using the Needleman andWunsch (J. Mol. Biol. (48): 444-453 (1970)) algorithm which has beenincorporated into the GAP program in the GCG software package (availableat URL accelrys[dot]com), using either a Blossom 62 matrix or a PAM250matrix, and a gap weight of 16, 14, 12, 10, 8, 6 or 4 and a lengthweight of 1, 2, 3, 4, 5 or 6. The skilled person will appreciate thatall these different parameters will yield slightly different results butthat the overall percentage identity of two sequences is notsignificantly altered when using different algorithms.

In yet another embodiment, the percent identity between two nucleotidesequences is determined using the GAP program in the GCG softwarepackage (available at URL accelrys[dot]com), using a NWSgapdna.CMPmatrix and a gap weight of 40, 50, 60, 70 or 80 and a length weight of1, 2, 3, 4, 5 or 6. In another embodiment, the percent identity betweentwo amino acid or nucleotide sequences is determined using the algorithmof E. Meyers and W. Miller (CABIOS, 4:11-17 (1989) which has beenincorporated into the ALIGN program (version 2.0) (available at URLvega[dot]igh[dot]cnrs[dot]fr[slash]bin[slash]aliqn-guess[dot]cgi) usinga PAM120 weight residue table, a gap length penalty of 12 and a gappenalty of 4.

The nucleic acid and protein sequences of the present invention mayfurther be used as a “query sequence” to perform a search against publicdatabases to, for example, identify other family members or relatedsequences. Such searches may be performed using the BLASTN and BLASTXprograms (version 2.0) of Altschul, et al. (1990) J. Mol. Biol.215:403-10. BLAST nucleotide searches may be performed with the BLASTNprogram, score =100, word length =12 to obtain nucleotide sequenceshomologous to the nucleic acid molecules of the present invention. BLASTprotein searches may be performed with the BLASTX program, score =50,word length =3 to obtain amino acid sequences homologous to the proteinmolecules of the present invention. To obtain gapped alignments forcomparison purposes, Gapped BLAST may be utilized as described inAltschul et al., (1997) Nucleic Acids Res. 25 (17): 3389-3402.

When utilizing BLAST and Gapped BLAST programs, the default parametersof the respective programs (e.g., BLASTX and BLASTN) may be used. SeeURL ncb[dot]nlm[dot]nih[dot]gov.

In another preferred embodiment, an isolated nucleic acid molecule ofthe invention comprises a nucleic acid molecule which is the complementof a nucleotide sequence as of the present invention, such as forinstance the sequence shown in SEQ ID NO:1. A nucleic acid molecule,which is complementary to a nucleotide sequence disclosed herein, is onethat is sufficiently complementary to a nucleotide sequence shown in SEQID NO:1 such that it may hybridize to said nucleotide sequence therebyforming a stable duplex.

In a further preferred embodiment, a nucleic acid of the invention asshown in SEQ ID NO:1 or the complement thereof contains at least onemutation leading to a gene product with modified function/activity. Theat least one mutation may be introduced by methods described herein. Inone aspect, the at least one mutation leads to a SMS 37 protein whosefunction and/or activity compared to the wild type counterpart isenhanced or improved. Methods for introducing such mutations are wellknown in the art.

The term “increase” of activity as used herein encompasses increasingactivity of one or more polypeptides in the producing organism, which inturn are encoded by the corresponding polynucleotides described herein.There are a number of methods available in the art to accomplishincrease of activity of a given protein, in this case the SMS 37protein. In general, the specific activity of a protein may be increasedor the copy number of the protein may be increased. The term increase ofactivity or equivalent expressions also encompasses the situationwherein SMS 37 protein activity is introduced in a cell that did notcontain this activity before, e.g. by introducing a gene encoding SMS 37in a cell that did not contain an equivalent of this gene before, orthat could not express an active form of the corresponding proteinbefore.

To facilitate such an increase, the copy number of the genescorresponding to the polynucleotides described herein may be increased.Alternatively, a strong promoter may be used to direct the expression ofthe polynucleotide. In another embodiment, the promoter, regulatoryregion and/or the ribosome binding site upstream of the gene can bealtered to increase the expression. The expression may also be enhancedor increased by increasing the relative half-life of the messenger RNA.In another embodiment, the activity of the polypeptide itself may beincreased by employing one or more mutations in the polypeptide aminoacid sequence, which increase the activity. For example, altering theaffinity of the polypeptide for its corresponding substrate may resultin improved activity. Likewise, the relative half-life of thepolypeptide may be increased. In either scenario, that being enhancedgene expression or increased specific activity, the improvement may beachieved by altering the composition of the cell culture media and/ormethods used for culturing. “Enhanced expression” or “improved activity”as used herein means an increase of at least 5%, 10%, 25%, 50%, 75%,100%, 200% or even more than 500%, compared to a wild-type protein,polynucleotide, gene; or the activity and/or the concentration of theprotein present before the polynucleotides or polypeptides are enhancedand/or improved. The activity of the SMS 37 protein may also be enhancedby contacting the protein with a specific or general enhancer of itsactivity.

Another aspect of the invention pertains to vectors, containing anucleic acid encoding a protein according to the invention or afunctional equivalent or portion thereof. As used herein, the term“vector” refers to a nucleic acid molecule capable of transportinganother nucleic acid to which it has been linked. One type of vector isa “plasmid”, which refers to a circular double stranded DNA loop intowhich additional DNA segments may be ligated. Another type of vector isa viral vector, wherein additional DNA segments may be ligated into theviral genome. Certain vectors are capable of autonomous replication in ahost cell into which they are introduced (e.g., bacterial vectors havinga bacterial origin of replication). Other vectors are integrated intothe genome of a host cell upon introduction into the host cell, andthereby are replicated along with the host genome.

Moreover, certain vectors are capable of directing the expression ofgenes to which they are operatively linked. Such vectors are referred toherein as “expression vectors”. In general, expression vectors ofutility in recombinant DNA techniques are often in the form of plasmids.The terms “plasmid” and “vector” can be used interchangeably herein asthe plasmid is the most commonly used form of vector. However, theinvention is intended to include such other forms of expression vectors,such as viral vectors (e.g., replication defective retroviruses,adenoviruses and adeno-associated viruses), which serve equivalentfunctions.

The recombinant vectors of the invention comprise a nucleic acid of theinvention in a form suitable for expression of the nucleic acid in ahost cell, which means that the recombinant expression vector includesone or more regulatory sequences, selected on the basis of the hostcells to be used for expression, which is operatively linked to thenucleic acid sequence to be expressed. Within a recombinant expressionvector, “operatively linked” is intended to mean that the nucleotidesequence of interest is linked to the regulatory sequence(s) in a mannerwhich allows for expression of the nucleotide sequence (e.g., in an invitro transcription/translation system or in a host cell when the vectoris introduced into the host cell). The term “regulatory sequence” isintended to include promoters, enhancers and other expression controlelements (e.g., attenuator). Such regulatory sequences are described,for example, in Goeddel; Gene Expression Technology: Methods inEnzymology 185, Academic Press, San Diego, Calif. (1990). Regulatorysequences include those which direct constitutive or inducibleexpression of a nucleotide sequence in many types of host cells andthose which direct expression of the nucleotide sequence only in acertain host cell (e.g. tissue-specific regulatory sequences). It willbe appreciated by those skilled in the art that the design of theexpression vector can depend on such factors as the choice of the hostcell to be transformed, the level of expression of protein desired, etc.The expression vectors of the invention may be introduced into hostcells to thereby produce proteins or peptides, encoded by nucleic acidsas described herein, including, but not limited to, mutant proteins,fragments thereof, variants or functional equivalents thereof, andfusion proteins, encoded by a nucleic acid as described herein, e.g.,SMS 37 proteins, mutant forms of SMS 37 proteins, fusion proteins andthe like.

The recombinant expression vectors of the invention may be designed forexpression of SMS 37 proteins in a suitable microorganism. For example,a protein according to the invention may be expressed in bacterial cellssuch as strains belonging to the genera Gluconobacter, Gluconacetobacteror Acetobacter. Expression vectors useful in the present inventioninclude chromosomal-, episomal- and virus-derived vectors e.g., vectorsderived from bacterial plasmids, bacteriophage, and vectors derived fromcombinations thereof, such as those derived from plasmid andbacteriophage genetic elements, such as cosmids and phagemids.

The DNA insert may be operatively linked to an appropriate promoter,which may be either a constitutive or inducible promoter. The skilledperson will know how to select suitable promoters. The expressionconstructs may contain sites for transcription initiation, termination,and, in the transcribed region, a ribosome binding site for translation.The coding portion of the mature transcripts expressed by the constructsmay preferably include an initiation codon at the beginning and atermination codon appropriately positioned at the end of the polypeptideto be translated.

Vector DNA may be introduced into suitable host cells via conventionaltransformation or transfection techniques. As used herein, the terms“transformation”, “transconjugation” and “transfection” are intended torefer to a variety of art-recognized techniques for introducing foreignnucleic acid (e.g., DNA) into a host cell, including calcium phosphateor calcium chloride co-precipitation, DEAE-dextran-mediatedtransfection, transduction, infection, lipofection, cationiclipidmediated transfection or electroporation. Suitable methods fortransforming or transfecting host cells may be found in Sambrook, et al.(supra), Davis et al., Basic Methods in Molecular Biology (1986) andother laboratory manuals.

In order to identify and select cells which have integrated the foreignDNA into their genome, a gene that encodes a selectable marker (e.g.,resistance to antibiotics) is generally introduced into the host cellsalong with the gene of interest. Preferred selectable markers includethose that confer resistance to drugs, such as kanamycin, tetracycline,ampicillin and streptomycin. A nucleic acid encoding a selectable markeris preferably introduced into a host cell on the same vector as thatencoding a protein according to the invention or can be introduced on aseparate vector such as, for example, a suicide vector, which cannotreplicate in the host cells. Cells stably transfected with theintroduced nucleic acid can be identified by drug selection (e.g., cellsthat have incorporated the selectable marker gene will survive, whilethe other cells die).

The invention provides also an isolated polypeptide having the aminoacid sequence shown in SEQ ID NO:2 or an amino acid sequence obtainableby expressing a polynucleotide of the present invention, such as forinstance a polynucleotide sequence shown in SEQ ID NO:1 in anappropriate host.

Polypeptides according to the invention may contain only conservativesubstitutions of one or more amino acids in the amino acid sequencerepresented by SEQ ID NO:2 or substitutions, insertions or deletions ofnon-essential amino acids. Accordingly, a non-essential amino acid is aresidue that may be altered in the amino acid sequences shown in SEQ IDNO:2 without substantially altering the biological function. Forexample, amino acid residues that are conserved among the proteins ofthe present invention, are predicted to be particularly unamenable toalteration. Furthermore, amino acids conserved among the proteinsaccording to the present invention and other SMS 37 proteins are notlikely to be amenable to alteration.

The term “conservative substitution” is intended to mean that asubstitution in which the amino acid residue is replaced with an aminoacid residue having a similar side chain. These families are known inthe art and include amino acids with basic side chains (e.g., lysine,arginine and histidine), acidic side chains (e.g., aspartic acid,glutamic acid), uncharged polar side chains (e.g., glycine, asparagine,glutamine, serine, threonine, tyrosine, cysteine), non-polar side chains(e.g., alanine, valine, leucine, isoleucine, proline, phenylalanine,methionine, tryptophan), beta-branched side chains (e.g., threonine,valine, isoleucine) and aromatic side chains (e.g., tyrosine,phenylalanine, tryptophan, histidine). As mentioned above, thepolynucleotides of the invention may be utilized in the geneticengineering of a suitable host cell to make it better and more efficientin the fermentation, for example in a direct fermentation process forVitamin C.

According to the invention a genetically engineered/recombinantlyproduced host cell (also referred to as recombinant cell or transformedcell) carrying such a modified polynucleotide wherein the function ofthe linked protein is significantly modified in comparison to awild-type cell such that the yield, production and/or efficiency ofproduction of one or more fermentation products such as Vitamin C isimproved. The host cell may be selected from a microorganism capable ofdirectly producing one or more fermentation products such as forinstance Vitamin C from a given carbon source, in particularGluconobacter oxydans, preferably G. oxydans DSM 17078.

A “transformed cell” or “recombinant cell” is a cell into which (or intoan ancestor of which) has been introduced, by means of recombinant DNAtechniques, a nucleic acid according to the invention, or wherein theactivity of the SMS 37 protein has been increased and/or enhanced.Suitable host cells include cells of microorganisms capable of producinga given fermentation product, e.g., converting a given carbon sourcedirectly into Vitamin C. In particular, these include strains from thegenera Pseudomonas, Pantoea, Escherichia, Corynebacterium,Ketogulonicigenium and acetic acid bacteria like e.g., Gluconobacter,Acetobacter or Gluconacetobacter, preferably Acetobacter sp.,Acetobacter aceti, Gluconobacter frateurii, Gluconobacter cerinus,Gluconobacter thailandicus, Gluconobacter oxydans, more preferably G.oxydans, most preferably G. oxydans DSM 17078.

Improved gene expression may also be achieved by modifying the SMS 37gene, e.g., by introducing one or more mutations into the SMS 37 genewherein said modification leads to a SMS 37 protein with a functionwhich is significantly improved in comparison to the wild-type protein.

Therefore, in one other embodiment, the polynucleotide carrying the atleast one mutation is derived from a polynucleotide as represented bySEQ ID NO:1 or equivalents thereof.

A mutation as used herein may be any mutation leading to a morefunctional or more stable polypeptide, e.g. more functional or morestable SMS 37 gene products. This may include for instance an alterationin the genome of a microorganism, which improves the synthesis of SMS 37or leads to the expression of a SMS 37 protein with an altered aminoacid sequence whose function compared with the wild type counterparthaving a non-altered amino acid sequence is improved and/or enhanced.The improvement may occur at the transcriptional, translational orpost-translational level.

The alteration in the genome of the microorganism may be obtained e.g.by replacing through a single or double crossover recombination a wildtype DNA sequence by a DNA sequence containing the alteration. Forconvenient selection of transformants of the microorganism with thealteration in its genome the alteration may, e.g. be a DNA sequenceencoding an antibiotic resistance marker or a gene complementing apossible auxotrophy of the microorganism. Mutations include, but are notlimited to, deletion-insertion mutations.

An alteration in the genome of the microorganism leading to a morefunctional polypeptide may also be obtained by randomly mutagenizing thegenome of the microorganism using e.g. chemical mutagens, radiation ortransposons and selecting or screening for mutants which are better ormore efficient producers of one or more fermentation products. Standardmethods for screening and selection are known to the skilled person.

In a specific embodiment, it is desired to knockout or suppress arepressor of the SMS 37 gene of the present invention, i.e., wherein itsrepressor gene expression is artificially suppressed in order to improvethe yield, productivity, and/or efficiency of production of thefermentation product when introduced into a suitable host cell. Methodsof providing knockouts as well as microorganisms carrying suchsuppressed genes are well known in the art. The suppression of therepressor gene may be induced by deleting at least a part of therepressor gene or the regulatory region thereof. As used herein,“suppression of the gene expression” includes complete and partialsuppression, as well as suppression under specific conditions and alsosuppression of the expression of either one of the two alleles.

The aforementioned mutagenesis strategies for SMS 37 proteins may resultin increased yields of a desired compound in particular Vitamin C. Thislist is not meant to be limiting; variations on these mutagenesisstrategies will be readily apparent to one of ordinary skill in the art.By these mechanisms, the nucleic acid and protein molecules of theinvention may be utilized to generate microorganisms such asGluconobacter oxydans or related strains of bacteria expressing mutatedSMS 37 nucleic acid and protein molecules such that the yield,productivity, and/or efficiency of production of a desired compound suchas Vitamin C is improved.

In connection with the above process using a microorganism, in oneaspect, the process of the present invention leads to yields of VitaminC which are in general at least about more than 5.7 g/l, such as 10 g/l,20 g/l, 50 g/l, 100 g/l, 200 g/l, 300 g/l, 400 g/l or more than 600 g/l.In one embodiment, the yield of Vitamin C produced by the process of thepresent invention is in the range of from about more than 5.7 to about600 g/l. The yield of Vitamin C refers to the concentration of Vitamin Cin the harvest stream coming directly out of the production vessel, i.e.the cell-free supernatant comprising the Vitamin C.

In one aspect of the invention, microorganisms (in particular from thegenera of Gluconobacter, Gluconacetobacter and Acetobacter) are providedthat are able to directly produce Vitamin C from a suitable carbonsource like D-sorbitol and/or L-sorbose. When measured for instance in aresting cell method after an incubation period of 20 hours, theseorganisms were found to be able to produce Vitamin C directly fromD-sorbitol or L-sorbose, even up to a level of 280 mg/l and 670 mg/lrespectively. In another aspect of the invention, a microorganism isprovided capable of directly producing Vitamin C in quantities of 300mg/l when starting from D-sorbitol or more or 800 mg/l or more whenstarting from L-sorbose, respectively when for instance measured in aresting cell method after an incubation period of 20 hours. Such may beachieved by increasing the activity of a STS polypeptide, preferably aSMS 37 polypeptide. The yield of Vitamin C produced from D-sorbitol mayeven be as high as 400, 600, 1000 mg/l or even exceed 1.5, 2, 4, 10, 20,50 g/l. The yield of Vitamin C produced from L-sorbose may even be ashigh as 1000 mg/l or even exceed 1.5, 2, 4, 10, 20, 50 g/l. Preferably,these amounts of Vitamin C can be achieved when measured by resting cellmethod after an incubation period of 20 hours.

As used herein, measurement in a “resting cell method” comprises (i)growing the cells by means of any method well know to the person skilledin the art, (ii) harvesting the cells from the growth broth, and (iii)incubating the harvested cells in a medium containing the substratewhich is to be converted into the desired product, e.g. Vitamin C, underconditions where the cells do not grow any longer, i.e. there is noincrease in the amount of biomass during this so-called conversion step.

The recombinant microorganism carrying e.g. a modified SMS 37 gene andwhich is able to produce the fermentation product in significantlyhigher yield, productivity, and/or efficiency may be cultured in anaqueous medium supplemented with appropriate nutrients under aerobicconditions as described above.

The nucleic acid molecules, polypeptides, vectors, primers, andrecombinant microorganisms described herein may be used in one or moreof the following methods: identification of Gluconobacter oxydans andrelated organisms; mapping of genomes of organisms related toGluconobacter oxydans; identification and localization of Gluconobacteroxydans sequences of interest; evolutionary studies; determination ofSMS 37 protein regions required for function; modulation of a SMS 37protein activity or function; modulation of the activity of a SMSpathway; and modulation of cellular production of a desired compound,such as Vitamin C.

The invention provides methods for screening molecules which modulatethe activity of a SMS 37 protein, either by interacting with the proteinitself or a substrate or binding partner of the SMS 37 protein, or bymodulating the transcription or translation of a SMS 37 nucleic acidmolecule of the invention. In such methods, a microorganism expressingone or more SMS 37 proteins of the invention is contacted with one ormore test compounds, and the effect of each test compound on theactivity or level of expression of the SMS 37 protein is assessed.

The biological, enzymatic or other activity of SMS proteins can bemeasured by methods well known to a skilled person, such as, forexample, by incubating a cell fraction in containing the SMS protein inthe presence of its substrate, electron acceptor(s) or donor(s)including phenazine methosulfate (PMS), dichlorophenol-indophenol(DCIP), NAD, NADH, NADP, NADPH, which consumption can be directly orindirectly measured by photometric, colorimetric or fluorimetricmethods, and other inorganic components which might be relevant for thedevelopment of the activity. Thus, for example, the activity ofmembrane-bound D-sorbitol dehydrogenase can be measured in an assaywhere membrane fractions containing this enzyme are incubated in thepresence of phosphate buffer at pH 6, D-sorbitol and the artificialelectron acceptors DCIP and PMS. The rate of consumption of DCIP can bemeasured at 600 nm, and is directly proportional to the D-sorbitoldehydrogenase activity present in the membrane fraction.

In case of transporters, such as e.g. importer, symporters or exporters,the activity of such SMS proteins can be measured by methods well knownto a skilled person, such as, for example, by incubating a membranefraction containing the SMS protein with the radioactively marked sugaror sugar alcohol which can be actively transported by the SMS protein.The activity of the transporter is directly proportional to (1) theamount of radioactivity incorporated into the cell mass, if the SMSprotein is involved in import of sugar or sugar alcohols into thecytoplasm or (2) the amount of radioactivity accumulated outside thecytoplasm into the periplasm/extracellular environment, if the SMSprotein is involved in export of sugar or sugar alcohols, such as e.g.sorbosone, outside the cytoplasm. Thus, for example, the activity of atransporter can be measured in an assay where intact cells containingthe specific transporter are incubated in the presence of phosphatebuffer at pH 6 and the radioactively marked carbon source such as e.g.glucose, galactose or sorbosone. The rate of assimilation of radioactivecarbon source such as e.g. glucose, galactose or sorbosone by the cellscan be measured by methods known to the skilled person, and is directlyproportional to the SMS protein activity present in the membranefraction, if the transport from outside into the cytoplasm should bemeasured. In the case of exporters, one can also generate invertedmembranes, e.g. inside-out vesicles and measure the uptake ofradioactivity as described above.

A further method of measuring the activity of exporters such as, e.g.SMS 37, may be via determination of the extracellular level of compoundsproduced in the cytoplasm, such as e.g. sorbosone, but which requireexport to the periplasm or extracellular environment performed by saidexporter and comparing this level to a situation wherein efflux systemis not present, such as e.g. knockout mutants wherein the gene encodingsaid exporter is not active any more, and thus extracellular levels maydecrease. In contrast, overexpression of such a gene encoding saidexporter may result in increased extracellular levels of the compoundsuch as, e.g. sorbosone.

It may be evident from the above description that the fermentationproduct of the methods according to the invention may not be limited toVitamin C alone. The “desired compound” or “fermentation product” asused herein may be any natural product of Gluconobacter oxydans, whichincludes the final products and intermediates of biosynthesis pathways,such as for example L-sorbose, L-sorbosone, D-gluconate,2-keto-D-gluconate, 5-keto-D-gluconate, 2,5-diketo-D-gluconate and2-keto-L-gulonate (2-KGA), in particular the biosynthetic generation ofVitamin C.

Thus, the present invention is directed to the use of a polynucleotide,polypeptide, vector, primer and recombinant microorganism as describedherein in the production of Vitamin C, i.e., the direct conversion of acarbon source into Vitamin C. In a preferred embodiment, a modifiedpolynucleotide, polypeptide, vector and recombinant microorganism asdescribed herein is used for improving the yield, productivity, and/orefficiency of the production of Vitamin C.

The terms “production” or “productivity” are art-recognized and includethe concentration of the fermentation product (for example, Vitamin C)formed within a given time and a given fermentation volume (e.g., kgproduct per hour per liter). The term “efficiency of production”includes the time required for a particular level of production to beachieved (for example, how long it takes for the cell to attain aparticular rate of output of a fermentation product). The term “yield”is art-recognized and includes the efficiency of the conversion of thecarbon source into the product e., Vitamin C). This is generally writtenas, for example, kg product per kg carbon source. By “increasing theyield and/or production/productivity” of the compound it is meant thatthe quantity of recovered molecules, or of useful recovered molecules ofthat compound in a given amount of culture over a given amount of timeis increased. The terms “biosynthesis” or a “biosynthetic pathway” areart-recognized and include the synthesis of a compound, preferably anorganic compound, by a cell from intermediate compounds in what may be amultistep and highly regulated process. The language “metabolism” isart-recognized and includes the totality of the biochemical reactionsthat take place in an organism. The metabolism of a particular compound,then, (e.g., the metabolism of an amino acid such as glycine) comprisesthe overall biosynthetic, modification, and degradation pathways in thecell related to this compound. The language “transport” or “import” isart-recognized and includes the facilitated movement of one or moremolecules across a cellular membrane through which the molecule wouldotherwise either be unable to pass or be passed inefficiently.

Vitamin C as used herein may be any chemical form of L-ascorbic acidfound in aqueous solutions, such as for instance undissociated, in itsfree acid form or dissociated as an anion. The solubilized salt form ofL-ascorbic acid may be characterized as the anion in the presence of anykind of cations usually found in fermentation supernatants, such as forinstance potassium, sodium, ammonium, or calcium. Also included may beisolated crystals of the free acid form of L-ascorbic acid. On the otherhand, isolated crystals of a salt form of L-ascorbic acid are called bytheir corresponding salt name, i.e. sodium ascorbate, potassiumascorbate, calcium ascorbate and the like.

In one preferred embodiment, the present invention is related to aprocess for the production of Vitamin C wherein a nucleotide accordingto the invention or a modified polynucleotide sequence as describedabove is introduced into a suitable microorganism, the recombinantmicroorganism is cultured under conditions that allow the production ofVitamin C in high productivity, yield, and/or efficiency, the producedfermentation product is isolated from the culture medium and optionallyfurther purified. Suitable host microorganisms may be selected from e.g.G. oxydans DSM 17078, G. oxydans IFO 3293, G. oxydans IFO 3292, G.oxydans ATCC 621H, G. oxydans IFO 12528, G. oxydans T-100 G. oxydans IFO3291, G. oxydans IFO 3255, G. oxydans ATCC 9937, G. oxydans ATCC 9937,G. oxydans IFO 3244, G. cerinus IFO 3266, G. frateurii IFO 3260, G.oxydans IFO 3287, G. thailandicus NBRC 100600 or Gluconoacetobacterliquefaciens ATCC 14835.

This invention is further illustrated by the following examples whichshould not be construed as limiting. The contents of all references,patent applications, patents and published patent applications, citedthroughout this application are hereby incorporated by reference.

EXAMPLES Example 1 Preparation of Chromosomal DNA and Amplification ofDNA Fragment by PCR

Chromosomal DNA of Gluconobacter oxydans DSM 17078 was prepared from thecells cultivated at 30° C. for 1 day in mannitol broth (MB) liquidmedium consisting of 25 g/1 mannitol, 5 g/l of yeast extract (Difco),and 3 g/l of Bactopeptone (Difco) by the method described by Sambrook etal (1989) “Molecular Cloning: A Laboratory Manual/Second Edition”, ColdSpring Harbor Laboratory Press).

A DNA fragment was prepared by PCR with the chromosomal DNA preparedabove and a set of primers, Pf (SEQ ID NO:3) and Pr (SEQ ID NO:4). Forthe reaction, the Expand High Fidelity PCR kit (Roche Diagnostics) and10 ng of the chromosomal DNA was used in total volume of 100 μlaccording to the supplier's instruction to have the PCR productcontaining SMS 37 DNA sequence (SEQ ID NO:1). The PCR product wasrecovered from the reaction and its correct sequence confirmed.

Example 2 Overexpression of the SMS 37 Gene in G. oxydans DSM 17078

To upregulate the expression of the SMS 37 gene, an overexpressionsystem using a plasmid construct was used. Herein, the SMS 37 gene wasfused to a strong constitutive promoter, and the construct was thenintroduced into G. oxydans DSM 17078. The overexpression of the SMS 37gene is determined through standard methods known to those skilled inthe art, such as transcript analysis using Northern Blot, RT-PCR orother technology, protein expression determination using Western Blot,two-dimensional gel electrophoresis, protein activity determinationusing specific enzyme assays or through direct measurement of productformation or substrate conversion.

The promoter can be any promoter that exhibits strong constitutiveactivity in Gluconobacter oxydans such as the tufB promoter fromEscherichia coli, the tufB promoter from Gluconobacter oxydans, the sldhpromoter from Gluconobacter oxydans, or the sndh promoter fromGluconobacter oxydans.

The plasmid for the plasmid-based overexpression system can be anyplasmid that is capable of replicating in both Escherichia coli andGluconobacter oxydans and which can be transferred between the twospecies. The plasmid may conveniently contain a selectable marker suchthat the transfer of such a plasmid can be monitored e.g.antibiotic-resistance marker, complementing marker for auxotrophy. Sucha plasmid can include, but is not limited to, pVK100, pGE1, pBBR1MCS-2,RSF1010 and their derivatives (vectors with catalog numbers orinformation source, pVK100=ATCC 37156, pGE1=J. Ferment Bioeng. 79, 95,1995, pBBR1MCS-2=NCCB 3434, RSF1010=NCCB 3110).

The entire SMS 37 gene was amplified by PCR using primer pair PsndhSMS37+1 (SEQ ID NO:5) containing complementary P_(sndh) promoter overhangsequence at the 5′-end and SMS 37HindIII-1 [SEQ ID NO:4 with GAGAAAGCTTat the 5′-end]. The P_(sndh) promoter (SEQ ID NO:6) was amplified by PCRusing primers PsndhXhoI+1 (SEQ ID NO:7) and SMS 37Psndh-1 (SEQ ID NO:8)containing complementary SMS 37 DNA overhang sequence at 5′-end. G.oxydans DSM 17078 genomic DNA was used as a template and the reactionconditions consisted of 35 cycles of denaturation at 94° C. for 30 sec,annealing at 50° C. for 30 sec and extension at 72° C. for 1 min. Inboth cases, the GC-rich PCR kit (Roche Molecular Biochemicals) was used.As the two fragments have complementary overhangs, the individual PCRfragments were mixed and re-amplified using the primer pairPsndhXhoI+1/SMS 37HindIII-1 to amplify a full length product whereby thechosen promoter was inserted upstream of the SMS 37 gene. The PCRreaction conditions for the second round reaction consisted of 94° C., 2min, then 10 cycles of [94° C., 30 sec, 63° C., 30 sec, 68° C., 6 min],followed by 20 cycles of [94° C., 30 sec, 63° C., 30 sec, 68° C., 6 minwith an additional 20 sec per cycle] and a final extension at 68° C. for10 min. The PCR product was purified and doubly-digested with XhoI andHindu and cloned into XhoI-HindIII-digested pVK100 vector. The ligationmix was transformed into E. coli TOP 10 cells and transformants wereselected for on Luria-Bertani agar containing tetracycline to a finalconcentration of 10 μg ml⁻¹. Putative transformants were screened bycolony PCR using primer pair PsndhXhoI+1/SMS 37HindIII-1. Positivetransformants were picked, plasmid minipreps made and the DNA sequenceof the insertion fragment was confirmed. Plasmids showing the correctsequence were transformed into competent G. oxydans DSM 17078 cellsselecting transformants on mannitol broth agar medium containingtetracycline to a final concentration of 10 μg ml⁻¹. Several putativetransformants were observed of which four were analyzed by PCR usingprimer pair PsndhXhoI+1/SMS 37HindIII-1 to verify the presence of theplasmid. All strains were found to contain the SMS 37 overexpressionplasmid and were named G. oxydans DSM 17078-SMS 37up1, G. oxydans DSM17078-SMS 37up2, G. oxydans DSM 17078-SMS 37up3 and G. oxydans DSM17078-SMS 37up4.

Example 3 Production of Vitamin C from D-Sorbitol Using Resting Cells

Cells of G. oxydans DSM 17078, G. oxydans DSM 17078-SMS 37up1, G.oxydans DSM 17078-SMS 37up2, G. oxydans DSM 17078-SMS 37up3 and G.oxydans DSM 17078-SMS 37up4 were grown at 27° C. for 3 days on No. 3BDagar medium containing 70 g/l D-sorbitol, 0.5 g/l glycerol, 7.5 g/lyeast extract (Difco), 2.5 g/l MgSO₄.7H₂O, 10 g/l CaCO₃ and 18 g/l agar(Difco).

Cells were scraped from the agar plates, suspended in distilled waterand used for resting cell reactions conducted at 30° C. with shaking at220 rpm. A series of reactions (0.5 ml reaction mixture in 5 ml reactiontubes) was carried out with 2% D-sorbitol in reaction mixtures furthercontaining 0.3% NaCl, 1% CaCO₃ and was incubated with cells at a finalconcentration of OD₆₀₀=10. After an incubation period of 20 hours,samples of the reaction mixtures were analyzed by high performanceliquid chromatography (HPLC) using an Agilent 1100 HPLC system (AgilentTechnologies, Wilmington, USA) with a LiChrospher-100-RP18 (125×4.6 mm)column (Merck, Darmstadt, Germany) attached to an Aminex-HPX-78H(300×7.8 mm) column (Biorad, Reinach, Switzerland). The mobile phase was0.004 M sulfuric acid, and the flow rate was 0.6 ml/min. Two signalswere recorded using an UV detector (wavelength 254 nm) in combinationwith a refractive index detector. In addition, the identification of theL-ascorbic acid was done using an amino-column (YMC-Pack Polyamine-II,YMC, Inc., Kyoto, Japan) with UV detection at 254 nm. The mobile phasewas 50 mM NH₄H₂PO₄ and acetonitrile (40:60).

An Agilent Series 1100 HPLC-mass spectrometry (MS) system was used toidentify L-ascorbic acid. The MS was operated in positive ion mode usingthe electrospray interface. The separation was carried out using aLUNA-C8(2) column (100×4.6 mm) (Phenomenex, Torrance, USA). The mobilephase was a mixture of 0.1% formic acid and methanol (96:4). L-Ascorbicacid eluted with a retention time of 3.1 minutes. The identity of theL-ascorbic acid was confirmed by retention time and the molecular massof the compound.

The supernatants of the reaction mixtures incubated with cells of mutantstrains G. oxydans DSM 17078-SMS 37up1, G. oxydans DSM 17078-SMS 37up2,G. oxydans DSM 17078-SMS 37up3 and G. oxydans DSM 17078-SMS 37up4contained an average of 2.8 g/l of Vitamin C compared to 1.0 g/l for G.oxydans DSM 17078.

Example 4 Presence of the SMS 37 Gene and Equivalents in Other Organisms

The presence of SEQ ID NO:1 and/or equivalents in other organisms thanthe ones disclosed herein before, e.g. organisms as mentioned in Table1, may be determined by a simple DNA hybridization experiment.

Strains of Acetobacter aceti subsp. xylinum IFO 13693 and IFO 13773 aregrown at 27° C. for 3 days on No. 350 medium containing 5 g/lBactopeptone (Difco), 5 g/l yeast extract (Difco), 5 g/l glucose, 5 g/1mannitol, 1 g/l MgSO₄.7H₂O, 5 ml/l ethanol, and 15 g/l agar. All otherAcetobacter, Gluconacetobacter and all Gluconobacter strains are grownat 27° C. for 3 days on mannitol broth (MB) agar medium containing 25g/1 mannitol, 5 g/l yeast extract (Difco), 3 g/l Bactopeptone (Difco),and 18 g/l agar (Difco). E. coli K-12 is grown on Luria Broth agarmedium. The other strains are grown on medium recommended by thesuppliers or according to methods known in the art. Genomic DNA isextracted as described by e.g. Sambrook et al., 1989, “MolecularCloning: A Laboratory Manual/Second Edition”, Cold Spring HarborLaboratory Press) from a suitable organism as, e.g. mentioned in Table1.

Genomic DNA preparations are digested with restriction enzymes such asEcoRI or HindIII, and 1 μg of the DNA fragments are separated by agarosegel electrophoresis (1% agarose). The gel is treated with 0.25 N HCl for15 min and then 0.5 N NaOH for 30 min, and then blotted ontonitrocellulose or a nylon membrane with Vacuum Blotter Model 785(BIO-RAD Laboratories AG, Switzerland) according to the instruction ofthe supplier. The resulting blot is then brought into contact/hybridizedwith a solution wherein the probe, such as e.g. a DNA fragment with SEQID NO:1 sequence or a DNA fragment containing the part or whole of theSEQ ID NO:1 sequence to detect positive DNA fragment(s) from a testorganism. A DIG-labeled probe, e.g. SEQ ID NO:1, may be preparedaccording to Example 1 by using the PCR-DIG labeling kit (RocheDiagnostics) and a set of primers, SEQ ID NO:3 and SEQ ID NO:4. A resultof such a blot is depicted in Table 1.

The hybridization may be performed under stringent or highly stringentconditions. A preferred, non-limiting example of such conditions arehybridization in 6× sodium chloride/sodium citrate (SSC) at about 45°C., followed by one or more washes in 1×SSC, 0.1% SDS at 50° C.,preferably at 55° C., more preferably at 60° C. and even more preferablyat 65° C. Highly stringent conditions include, for example, 2 h to 4days incubation at 42° C. in a solution such as DigEasyHyb solution(Roche Diagnostics GmbH) with or without 100 μg/ml salmon sperm DNA, ora solution comprising 50% formamide, 5×SSC (150 mM NaCl, 15 mM trisodiumcitrate), 0.02% sodium dodecyl sulfate, 0.1% N-lauroylsarcosine, and 2%blocking reagent (Roche Diagnostics GmbH), followed by washing thefilters twice for 5 to 15 min in 2×SSC and 0.1% SDS at room temperatureand then washing twice for 15-30 min in 0.5×SSC and 0.1% SDS or 0.1×SSCand 0.1% SDS at 65-68° C. To detect DNA fragments with lower identity tothe probe DNA, final washing steps can be done at lower temperaturessuch as 50-65° C. and for shorter washing time such as 1-15 min.

The genes corresponding to the positive signals within the respectiveorganisms shown in Table 1 can be cloned by a PCR method well known inthe art using genomic DNA of such an organism together with a suitableprimer set, such as e.g. SEQ ID NO:3 and SEQ ID NO:4 under conditions asdescribed in Example 1 or as follows: 5 to 100 ng of genomic DNA is usedper reaction (total volume 50 μl). Expand High Fidelity PCR system(Roche Diagnostics) can be used with reaction conditions consisting of94° C. for 2 min; 30 cycles of (i) denaturation step at 94° C. for 15sec, (ii) annealing step at 60° C. for 30 sec, (iii) synthesis step at72° C. for 0.5 to 5 min depending to the target DNA length (1 min/1 kb);extension at 72° C. for 7 min. Alternatively, one can perform a PCR withdegenerate primers, which can be synthesized based on SEQ ID NO:2 oramino acid sequences as consensus sequences selected by aligning severalamino acid sequences obtained by a sequence search program such asBLASTP (or BLASTX when nucleotide sequence is used as a “querysequence”) to find proteins having a similarity to the protein of SEQ IDNO:2. For PCR using degenerate primers, temperature of the secondannealing step (see above) can be lowered to 55° C., or even to 50-45°C. A result of such an experiment is shown in Table 1.

Samples of the PCR reactions are separated by agarose gelelectrophoresis and the bands are visualized with a transilluminatorafter staining with e.g. ethidium bromide, isolated from the gel and thecorrect sequence is confirmed.

Consensus sequences mentioned above might be amino acid sequencesbelonging to certain categories of several protein domain/familydatabases such as PROSITE (database of protein families and domains),COGs (Cluster of Ortholog Groups), CDD (Conserved Domain Databases),pfam (large collection of multiple sequence alignments and hidden Markovmodels covering many common protein domains and families). Once one canselect certain protein with identical/similar function to the protein ofthis invention from proteins containing domain or family of suchdatabases, corresponding DNA encoding the protein can be amplified byPCR using the protein sequence or its nucleotide sequence when it isavailable in public databases. Following organisms may further providegenes, which can be used as an alternative gene of this invention:Shigella flexneri 2a strain 301, Salmonella typhimurium LT2, Bacillussubtilis 168, Agrobacterium tumefaciens C58, Bradyrhizobium japonicumUSDA 110, Sinorhizobium meliloti 1021 or Mesorhizobium loci MAFF303099.

Example 5 Overexpression of the SMS 37 Gene and Equivalents from OtherOrganisms for Production of Vitamin C

In order to improve Vitamin C production in a suitable microorganismwhich is capable to directly produce Vitamin C from a given substrate,the SMS 37 gene and equivalents as, e.g. a PCR product obtained inExample 4, referred to herein as gene X, can be used in anoverexpression system according to Example 2 or can be cloned intopCR2.1-TOPO (Invitrogen, Carlsbad, Calif., USA) and used to transform E.coli TG1 to have a Ap^(r) transformant carrying pCR2.1-TOPO-gene X, i.e.carrying a PCR product obtained in Example 4. The insert is amplifiedwith a set of primers, PfNdeI [SEQ ID NO:3 with CCCAT at the 5′-end] andPrHindIII [SEQ ID NO:4 with CCAAGCTT at the 5′-end], by PCR. ResultingPCR product is digested with NdeI and HindIII and the fragment isinserted together with PcrtE-SD (Shine-Dalgarno) fragment (WO 02/099095)digested with XhoI and NdeI into pVK100 (ATCC 37156) between the sitesof XhoI and HindIII. E. coli TG1 is transformed with the ligationproduct to have Tc′ transformant carrying plasmid pVK-PcrtE-SD-gene X,which is then used to transform a suitable host, e.g. G. oxydans DSM17078 by electroporation to have e.g. Ter G. oxydans DSM17078/pVK-PcrtE-SD-gene X.

Production of Vitamin C using the recombinant cells of e.g. G. oxydansstrains DSM 17078 and the corresponding wild-type strain are performedaccording to Example 3.

In the resting cell reaction with 1% L-sorbosone as the substrate, therecombinant cells can produce at least more than 20% Vitamin C comparedto the wild-type strain.

TABLE 1 Equivalents of the SMS 37 gene in other organisms. Strain Signal1 Signal 2 Signal 3 G. oxydans DSM 17078 ++++ + + G. oxydans IFO 3293++++ + + G. oxydans IFO 3292 ++++ + + G. oxydans ATCC 621H ++ + + G.oxydans IFO 12528 ++ + + G. oxydans G 624 + − + G. oxydans T-100++++ + + G. oxydans IFO 3291 + − + G. oxydans IFO 3255 + − + G. oxydansATCC 9937 + − + G. oxydans IFO 3244 + − + G. cerinus IFO 3266 + − + G.frateurii IFO 3260 + − + G. oxydans IFO 3287 + − + Acetobacter acetisubsp. orleanus IFO 3259 − − + Acetobacter aceti subsp. xylinum IFO13693 − − + Acetobacter aceti subsp. xylinum IFO 13773 − − + Acetobactersp. ATCC 15164 − − + G. thailandicus NBRC 100600 + − + Gluconacetobacterliquefaciens ATCC 14835 ++ − + Gluconacetobacter polyoxogenes NBI 1028 +− + Gluconacetobacter diazotrophicus − − + ATCC 49037 Gluconacetobactereuropaeus DSM 6160 − − + Acetobacter aceti 1023 − − + Acetobacterpasteurianus NCI 1193 − − + E. coli − − − Saccharomyces cerevisiae − − −Aspergillus niger − − − Mouse − − − Signal 1: Detection of DNA on a blotwith genomic DNA of different strains and SEQ ID NO: 1 as labeled probe.Signal 2: Detection of DNA of different strains in a PCR reaction usingprimer pair SEQ ID NO: 3 and SEQ ID NO: 4. Signal 3: Detection of DNA ofdifferent strains in a PCR reaction using degenerate primers. For moreexplanation refer to the text.

We claim:
 1. A method for the production of Vitamin C, said methodcomprising (a) culturing a recombinant Gluconobacter oxydans in anaqueous medium under conditions that allow direct production of VitaminC from D-sorbitol or L-sorbose, wherein the recombinant Gluconobacteroxydans has been transformed with an isolated polynucleotide operablylinked to at least one expression control sequence, wherein thepolynucleotide is selected from the group consisting of : (i) anucleotide sequence encoding the polypeptide as set forth in SEQ IDNO:2; and (ii) the nucleotide sequence set forth in SEQ ID NO:1; andwherein said polynucleotide is overexpressed in said Gluconobacteroxydan; and (b) isolating Vitamin C as product of said culturing;wherein at least 2.8 times more vitamin C is produced as compared to awild type Gluconobacter oxydans that do not overexpress saidpolynucleotide.
 2. The process according to claim 1, wherein theGluconobacter oxydans is capable of directly producing Vitamin C fromD-sorbitol in quantities of 300 mg/l or more when measured in a restingcell method after an incubation period of 20 hours.
 3. The processaccording to claim 1, wherein the Gluconobacter oxydans is capable ofdirectly producing Vitamin C from L-sorbose in quantities of 800 mg/l ormore.
 4. The process according to claim 1, wherein said Gluconobacteroxydans is Gluconobacter oxydans DSM 17078.